I consider the value of it being anonymous right now to be unknown or undefined. In the same way, I consider the value of it being non-anonymous right now to also be unknown or undefined. Since disclosure can only flow in one direction, I'm not aware of any reason to irrevocably transfer from one state to the next.
> I can use it to prove that I possessed certain files at certain times, historically.
Your twitter account would no longer be anonymous at that point. What's the utility of it being anonymous now?