It seems like the data should only be collected from the point forward after all current users sign a new agreement to allow it. It would be like Free Republic allowing OpenAI to have access to all the posts from the beginning of time.
Not that I don’t think there isn’t some AI somewhere spying on Free Republic.
In the early days a meta tag “NO ROBOTS, NO FOLLOW” would supposedly keep an HTML page from being indexed and showing up in search results. I just found an old page of mine from the 1990s that, of course, showed up in the search results. :^)