Thank you for pointing that out. I KNEW I had seen something about Hikitsuchi Sensei relating to this topic recently, and have been racking my brain all day to find it! 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?
PS - You threw me with your new username, at first I thought someone was stealing your research!