I read Mr. Pranin's response in that thread to mean that Hikitsuchi Sensei did have a certificate signed by O Sensei, but that it wasn't processed through the normal channels at Aikikai Hombu. Did you read it that way also?
KAMI : You're correct!
PS - You threw me with your new username, at first I thought someone was stealing your research!
KAMI : Well, if that was the case, I should've been proud, don't you think? After all, only valuable things are stolen...Unhappily, as you observed, that was not the case.