I don't think this particular piece of paper will "prove" anything to anyone who does/does not want to believe? If it goes into detail about you, I would simple block that out. But I don't see why a simple word conversation with your son that you were telling the truth becuause "your father's abuse of me" without detail shouldn't suffice?

You say your sons are old enough; what age are they now? Are they asking to see their father or is there some other pressure like that going on? I would not give in to pressure from anyone; at that time you did the best you could for your sons and it can't be undone now. If your sons are 18 and want to see their father, etc. more power to them; tell them the story verbally and if they believe your ex- over you there's not a lot you can do about that? You know you did not lie; that's all there is! The past cannot be changed in any event; even had you been the baddie and lied. The law and those set up to protect the innocent sided with you; that, in my book, is quite alot whether or not I know the person telling the story? There was a genuine issue there, not a he-said/she-said argument.