It's an opinion until it's available to his legal team
You are naive if you think that information is IMPOSSIBLE to find
You're confused on what you are trying to prove. Finding a document that is signed and dated BEFORE the trial, which is apparently what has come up, doesn't prove she lied about forgetting when it was signed.
Finding the signed dated document would only prove her a liar if she had said she'd signed it AFTER the trial. But she didn't, she said she didn't remember.