Case Study Blueprint: How a Brand Used Redirect Routing to Maintain Attribution During a Major Site Migration

Hook: The migration that broke attribution — and how you can avoid it

Site migrations are a predictable headache: SEO risk, broken links, and — critically for marketers — lost paid attribution. In 2026, with stricter privacy rules, cookieless attribution methods, and ad platforms enforcing stricter landing URL checks (updates rolled out through late 2025), a migration can erase weeks of campaign data if redirects aren’t mapped and tested. This guide is a templated case-study blueprint: how one brand preserved SEO and paid attribution during a major site migration, and exactly how you can document and replicate those steps.

Executive summary — what this template gives you

• Step-by-step migration playbook focused on redirect mapping and attribution preservation.
• A ready-to-use redirect map CSV template and sample rules (regex and wildcard formats).
• Pre-, during-, and post-migration audit checklists tied to measurable KPIs.
• Metrics and visualizations to include in your case study for internal stakeholders and agencies.
• 2026-specific tactics: server-side tagging (GTM Server or equivalent), click ID persistence, and real-time redirect controls.

Why this matters in 2026

By late 2025 and into 2026, three trends made migrations riskier and more visible:

1. Cookieless attribution and aggregated measurement: reliance on first-party data and server-side event collection accelerated. Losing query params or click IDs during redirects now has greater attribution impact.
2. Ad platform validation: Google Ads and other platforms increased checks on final landing URLs to prevent cloaking and misleading redirects — misconfigured redirects can trigger disapprovals or serve errors.
3. Real-time routing expectations: marketers want geo/device/A/B redirects during campaigns without developer cycles. Migrations that remove these controls can break campaign experiments.

Case snapshot (fictionalized, replicable)

Brand: BrightCart (mid-market e-commerce). Scope: domain change (www.brightcart.com -> shop.brightcart.com) plus product URL structure overhaul. Duration: 8-week migration window, staged rollout. Goal: preserve organic visibility and maintain paid attribution for holiday campaigns with minimal disruption.

Outcomes (headline)

• Organic sessions: -1.5% vs. baseline (7-day smoothing)
• Paid clicks attributed: +0.8% (no measurable drop after switch)
• Conversion rate (site-wide): +2.1% (improved page speed & tagging)
• 404 rate: Zero persistent 404s after automated redirect repairs

Pre-migration: the preparation checklist

Preparation eliminates surprises. Use this checklist as your gating criteria before any DNS or CMS changes.

Inventory and crawl

• Full site crawl export (Screaming Frog / Sitebulb) with status codes, canonical tags, and hreflang entries.
• Export URL index from Google Search Console (GSC): pages indexed and last crawl date.
• Backlink list export (Ahrefs/Majestic/GA4 referral reports) for high-value inbound pages (top 1,000).

Redirect map and rule design

Create a master redirect map CSV with these columns. This is your single source of truth during the migration.

• old_url — full old path (including query examples when relevant)
• new_url — target canonical URL
• status_code — 301/302
• pattern_type — exact/regex/wildcard
• preserve_query — true/false
• note — reason or owner

<!-- Sample rows -->
old_url,new_url,status_code,pattern_type,preserve_query,note
/collection/summer-2025,/collections/summer-25,301,exact,true,legacy landing pages
/products/(.*),/shop/product/$1,301,regex,true,product slug normalization
/search?q=(.*),/search?q=$1,302,regex,true,staged redirect to track experiments

Key decisions on status codes

Default to 301 for permanent moves to preserve SEO equity. Use 302 for short-term experiments or staged rollouts. In 2026, because of faster indexation and platform checks, mark temporary redirects explicitly and track their lifecycle.

Attribution and tracking preparation

• Inventory all click IDs and parameters used by campaigns (gclid, fbclid, wbraid, UTM_*).
• Ensure redirects preserve query strings or capture them at server-side (via server logs or redirect middleware).
• Enable server-side tagging (GTM Server or equivalent) to capture and persist click IDs into a first-party cookie or session storage.
• Coordinate with ad platforms: update final URLs in campaigns where necessary before the switch window to avoid landing page errors.

Migration day: operational playbook

Runbook and stakeholders

• Assign roles: Migration lead, Redirect engineer, SEO owner, Campaign analyst, DevOps, and Communications owner.
• Runbook steps with timestamps and rollback triggers (e.g., if organic sessions drop >10% within 24 hours rollback DNS).

Staged rollout

Deploy redirects in stages: core pages first (homepage, top 100 product pages, checkout flows), then secondary pages, then catch-alls. This reduces mass index churn and isolates issues.

Verification and smoke tests

1. Automated curl checks: verify 200/301/302 status and that query strings are preserved.
2. Run a full crawl of the new domain and compare against the master redirect map.
3. Verify server logs show captured click IDs on redirected requests (GCLID/gclid present in server logs or forwarded to tracking endpoint).
4. Check ad platform landing page approvals and serve status.

Post-migration: auditing & recovery checklist

Measure, detect, and fix. This is where many migrations either win or fail.

Immediate 0–72 hour checks

• Index coverage in GSC: monitor for spikes in excluded pages or sudden drops.
• Search impressions and clicks (7-day vs. baseline): look for outliers.
• 404 errors: identify and add missing redirects to the map (prioritize by referral and traffic volume).
• Paid attribution: compare click-to-conversion matching rate (GCLID/G/Server-side match) vs. baseline.

7–30 day health checks

• Organic sessions and keyword rankings: 14-day smoothing to account for index propagation.
• Backlink validation: ensure high-value referring domains land on appropriate pages (use link redirect audit).
• Conversion funnels: verify multi-touch attribution models to ensure last-click and first-click reflect expected flows.
• Redirect chain analysis: eliminate chains longer than 2 hops to preserve crawl budget and reduce latency.

What to document in your migration case study

Your stakeholders want clarity: what changed, why, and measured impact. Use this structure for the case study itself.

1. Executive summary

Short, data-backed headline results (e.g., "Organic sessions held steady; paid attribution preserved; conversion rate improved +2.1%").

2. Scope and timeline

Domain change, URL reformat, content merges, redirects volume, stakeholders, and exact dates.

3. Redirect map snapshot

Include an anonymized CSV excerpt and a visual flow diagram showing high-volume paths. Call out regex rules and critical exceptions (e.g., legacy landing pages with query-based promos).

4. Audit checks and tools used

• Tools: Screaming Frog, Sitebulb, GSC, GA4 (BigQuery export), server logs, ad platform reports.
• Tests: curl + header checks, simulated user journeys, device/geo checks, page speed and Core Web Vitals.

5. KPI before/after with windows & smoothing

• Baseline period: 28 days pre-migration.
• Short-term measurement: 7–14 days post-migration (with rolling averages).
• Long-term recovery window: 28–90 days post-migration.
• KPIs: organic sessions, paid clicks, conversion rate, revenue per session, 404 count, index coverage, backlink landing accuracy, attribution match rate (click ID persistence).

6. Root-cause and remediation notes

Document any mistakes: missing preserve_query flags, regex edge cases, or third-party redirects. Include remediation and the exact code or rule used to fix the issue.

7. Lessons learned & next steps

Operational changes, e.g., maintain a live redirect map in a shared repo, schedule quarterly redirect audits, and adopt version-controlled redirect maps for future migrations.

Sample redirect rules (safe, copyable examples)

Use these as starting points; test them in staging.

<!-- Preserve querystring and redirect product slugs -->
RewriteEngine On
RewriteRule ^/products/(.*)$ /shop/product/$1 [R=301,L,QSA]

<!-- Redirect old collection structure to new collections -->
RedirectMatch 301 ^/collection/(.*)$ /collections/$1

<!-- Catch-all: keep path but change domain, preserve query -->
# On old domain webserver
RewriteCond %{HTTP_HOST} ^www\.brightcart\.com$ [NC]
RewriteRule ^(.*)$ https://shop.brightcart.com/$1 [R=301,L,QSA]

Troubleshooting common pitfalls

• Lost UTM or click IDs: Confirm QSA (query string append) flags or implement server-side capture to persist the parameter in a first-party cookie before redirecting.
• Redirect chains: Use automated scripts to detect 301→301 chains and collapse to single hop rules; see guidance on redirect platform safety.
• Ad disapprovals: Ensure final URLs in ad accounts match the canonical destination and that any temporary 302s are documented and within platform policy.
• Unexpected indexing drops: Check robots.txt and meta-robots; sometimes new CMS defaults block crawlers.

Attribution-specific metrics and how to calculate them

These are the numbers your marketing team will ask for. Capture them with BigQuery exports or server logs where possible.

1. Click ID match rate: % of paid clicks where click ID (gclid/fbclid/wbraid) persisted to conversion. Calculate: matched_conversions / total_clicks_from_ads.
2. Landing match rate: % of top 1,000 backlinks mapping correctly to new URLs.
3. Redirect latency impact: median additional time added by redirect (ms). Measure via synthetic tests and server logs.
4. 404 impact score: weighted by referral and organic traffic volume to each missing page.

2026 advanced strategies (what the best teams are doing)

• Server-side routing & redirects: handle redirects at the edge (CDN/edge functions) to reduce latency and preserve query parameters reliably.
• Real-time redirect controls: allow marketing to add temporary redirect rules (geo/A/B) without deployments — useful for campaign experiments during migrations.
• AI-based anomaly detection: early-2026 tools flag drops in click ID match rate or unnatural 404 patterns within hours.
• Version-controlled redirect maps: store your CSVs in Git with deployable tags to trace changes and rollback quickly (tie this into authorization and deployment patterns).

How to present results to stakeholders

Keep it visual and bite-sized:

• One-line executive result + dashboard screenshot.
• Redirect map visual for the top 100 pages (before/after flows).
• Table of KPIs with % change and confidence windows (7/28/90 days).
• List of remedial changes with owners and dates.

Pro tip: Provide a short "What we would do differently" section. Honesty builds trust and speeds future approvals.

Downloadable templates (what to include)

• Master redirect map CSV (columns listed above).
• Migration runbook with roles, rollback triggers, and contact info.
• Post-migration KPI dashboard template (GA4 + BigQuery + Looker/Looker Studio).
• Audit checklist (pre/during/post) in a checklist format for ops teams.

Final checklist before you publish your case study

1. Verify data windows and smoothing has been documented (avoid premature conclusions).
2. Confirm link anonymization if sharing redirect rules publicly.
3. Include a concise recommended action plan (next 90 days) with owners.
4. Archive the full redirect map and test logs for future audits.

Closing thoughts & next steps

Migrations in 2026 are not just technical events; they are marketing events. Preserving SEO and paid attribution requires a structured redirect map, server-side tracking patterns that persist click IDs, and a rigorous audit process both before and after launch. Documenting the migration as a case study — with the redirect maps, audit checks, and metric baselines — is the fastest way to prove value and reduce risk for the next project.

Call to action

Ready to run a migration that preserves SEO and paid attribution? Download our free master redirect map CSV and migration runbook, or schedule a 30-minute migration audit to get a custom plan for your site. If you want the exact templates used in this guide, request the migration kit or contact our team to run a pre-migration simulation.

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