Good question.
I'd say it depends on how extraordinary the claim is, or beyond reasonable doubt, and if their is any opposition or debate of the validity..

I believe I can reasonably prove that I used cryptsy right to the end with TXs but can't really prove a final balance, I'm not sure their is reasonable doubt to doubt my statement (or even anyone unreasonably doubting), their is also no opposition and likely never will be, nor any debate of the validity..

I think even the receivership accepted about that amount of "proof", so if you like US law as a standard (I don't) I think my claim would fly if requested to prove it, but I didn't go through that because it was a small amount.

Someone who was named in the receivership might have slightly better "proof" with a court having granted them a portion of recovered value, but even that isn't solid blockchain proof because that's what you get for sending coins to a 3rd party.. That would just be trusting a court's opinion, and who trusts a court? Much less a courts opinion on altcoins, lol.

LOL @ FH and your welcome for a non-QS opinion, there's mine but I did it so I might be biased toward myself..