We can tell if an account has been migrated to steam or not yet. If it hasn’t been migrated to steam then we know they haven’t logged in since the steam switch went 100%.
So I know that we can kinda tell one way for this one cutoff that just so happens to line up with their event.
I’m not sure if they can check the actual log in dates but you can use another thing and logic to get enough info in this specific situation at least.