Public-facing date for when a user progressed past TL0

Our Discourse forum is semi-private. A number of our categories are public for viewing, but TL0 users cannot post in any section, send PMs, etc. I’m not sure how many of Discourse’s customers use Discourse for private forums, but if there are a significant number of them, it’d be great if join dates on profiles could accommodate private forums.

Right now if I want to see when a member was added to the forums, I have to guess based off of their posts (which may be inaccurate if they rarely post or don’t have any), as join date is for when they signed up – not when they were invited to post on the forums. There could be a potential problem where “What do we do if they were added, demoted to TL0, and then re-promoted?”: the first time they were invited would be more useful for my needs as I want to know how long they’ve been a part of the community, rather than a changelog of their trust level. Would be great to hear others’ use cases / opinions though.

A similar problem:

The RSS has dates for recent ones. So the number is stored, even if it is hard to find. I believe the date is the most recently one if someone was demoted and repromoted, but I’m not certain.