Thanks, I am familiar with HTTP caching and the way headers are used.
The issue started for me when working with existing search platforms/plugins acting as web spiders (so indexing the pages from the outside, without direct access to the discourse DB), which seem incapable of extracting the last update date from Discourse and rely instead on the Last Modified date.
I think I might work around this by adding a “published” meta tag and forcing the plugins to use that date.
Thanks for the help.