Can ownership be proven by help of an mirroring website & signing address

[guy_wonderful]

Hello!
Fellow Legendary account got stolen and we try to retrieve it.

You could know about that bitcointalk.to site.
Site who looks like a mirror of bitcointalk.org forum. It's copies all the posts, including those which are deleted.
Similar to web cache.

Post which had a signature and btc address in it, was deleted on the forum and is not accessible via any caches. But that post including btc address still appears on .to site.
Can a post from .to site, used to prove ownership of .org acc?

Thanks!