We might do this a bit overkill, but we automatically backup all comments on the application thread on the group website (if someone deletes them, we will still have a copy) + automatically make a hidden profile on the site for them which saves basic info like that. On top of that I do also have a separate spreadsheet with every single Steam join request and every single discussion top comment (so I can easily keep track which join requests are still pending) which also saves the Steam ID. So even if someone changes their name or deletes and remakes their account and have ever interacted with PA in any way I will always know what they did and when they did it.