But that's exactly what I meant:

I am all for a very transparent "published at" and "last updated at"

BUT NOT in the URL

Because either you would update the URL to the last updated_at (which leads to complications if updated often, need to keep a 302 for each updated/outdated url although it's not moved permanently, rather temporarily until next update)

Or you would be stuck with the original published date in the URL and potential readers could dismiss it based on a wrong assumption (that it's outdated)

An alternative is to keep posting new entries for every update, but that gets annoying as well, because you still need to show somehow that the old versions are not the newest.

So I totally agree to be upfront about original publishing date as well as last update date, but I would not put it in the URL, not for blog posts or any other page.