No Superbird fender tag has A13 on it. U or V confirms it's a Bird right off the bat by having a 440 engine noted in the VIN. A13 is only on the broadcast sheets. They didn't give Superbirds there own R"X" number.
I don’t know much about Superbirds, except that I want one. Thanks for the info, I’m always happy to be enlightened with more information! Drive on, brother!