Also, how does friedcat validate that someone owns shares when they hold an auction here on the forum if he doesn't track usernames of shareholders?
By signing a message from the address in the database.
Sure, that's how it could (and maybe should) be done, but according to TAT's escrow agreement from my last share purchase:
"Friedcat does not normally require signing a message from the Seller's shareholding wallet, but you are welcome to do so when requesting the transfer."
This seems to indicate that he is tracking the usernames of current shareholders and if he receives a PM from that username requesting that a number of shares be transferred to a different bitcoin address, then he complies.
What if a shareholder dies and one of their descendants wants to sell the share or have the e-mail address changed?
Or a shareholder gets banned from Bitcointalk.org and doesn't have access to PM anymore?