If you read the Google docs on XML Sitemaps and look at the lastmod field, Google says "Google reads the lastmod value, but if you misrepresent this value, we will stop reading it." Lily Ray asked John Mueller of Google if changing the lastmod date of a page too often will cause issues.
Here are the posts on Twitter:
I don't think you'd add commas at scale :), I wouldn't worry about it for individual pages, even if you have a bunch of things you end up updating regularly.
— 🍌 John 🍌 (@JohnMu) August 27, 2020
It is an interesting question because some CMS platforms, as Lily points out, can accidentally update the lastmod dates across many pages without anyone noticing and with minor changes. That can ultimately potentially lead to Google ignoring the lastmod information sent in the XML sitemap for that site.
John clarified "Do you mean the date in the markup on the page or the date in the sitemap file? I think folks are mixing things up a bit. For a sitemap file, any change in the page's primary content is fine to flag - it's purely about recrawling changes."
Do you mean the date in the markup on the page or the date in the sitemap file? I think folks are mixing things up a bit. For a sitemap file, any change in the page's primary content is fine to flag - it's purely about recrawling changes.
— 🍌 John 🍌 (@JohnMu) August 27, 2020
(this thread has gotten better, but different :-))
— 🍌 John 🍌 (@JohnMu) August 27, 2020
For SD, I'd use significant content updates (since that's shown & would be misleading otherwise). For Sitemaps, any change that requires recrawling is fine to flag. I doubt you'd notice a difference in SEO.
Will Google ignoring the lastmod date in an XML Sitemap end up hurting the site? Probably not in terms of ranking but if you want to push content or updates to content to Google faster, it can help if Google trusted your lastmod data information.
Forum discussion at Twitter.
