Your Last Deploy Reset Every Cache Validator on the Site
A post untouched since October reports Last-Modified as yesterday. Its ETag is just file mtime and size in hex, so one deploy voids every 304 you could earn.
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crawling
2 posts
In sitemap.xml, lastmod Is the Only Field Google Actually Reads
Ship priority 1.0 with changefreq always and Google drops both. The only field it uses is lastmod, and only when verifiably accurate. I ran three sitemaps through the official XSD to see what really counts.