Hypothesis. A real, stable <lastmod> (the genuine date a page’s content last changed) should make Googlebot recrawl and index pages better than a generic lastmod=now — testing the claim that “lastmod is the only tag that matters”.
Protocol. ~29,500 long-tail URLs (/ville/[cp]/[city] and /materiaux/[slug]/[cp]/[city]) split 50/50 by deterministic URL hash. Group A (control) served lastmod=now; Group B (treatment) served the real last-change date. Ran 41 days from 2026-04-21. Recrawl was measured directly from Googlebot hits in the nginx access logs over the full window (190,074 crawls, full coverage), with GSC indexation/traffic as secondary.
Findings. No measurable effect. Where the treatment was genuinely applied (B = old stable date vs A = now), Googlebot recrawl was identical: 5.53 vs 5.54 hits/URL (p=0.95) and 4.50 vs 4.51 distinct crawl-days/URL (p=0.99). The full-population result matches (6.48 vs 6.43, p=0.63), and the strongest-contrast subset slightly favored the control. Indexation was untestable — both arms sit at a ~99.6% ceiling.
International SEO Consultant (Freelance)
Founder of Kelogs, a SaaS SEO Crawler & Log Analyzer
Over 15 years of SEO experience
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