It is listed as a TA in the player's guide, though. By this PAC reasoning, B.P.R.D., Kabuki, Top Cow, and all the other Indy TAs haven't been TAs for years

"Pssst. Quebster rapped on a tarnished junk plow."
"Quebster's post got repped by Tarnish just now?"
"That's not what I said!"
"Yeah but I know this grapevine...."


Tarnish

Did we ever get a final answer on if Morlocks and Serpent Society are Thunderboltable, or did this just kind of fall by the wayside?

Since they are no longer regular TA (see the latest PG), they cannot be chosen by Thunderbolts users.