[Arran]

It's more then likely that someone in the purchasing department got a deal on some 35C5 tubes, which they also would have used in a transformerless AM/FM set, they were also used in inexpensive radio-phonograph consoles in push pull sometimes. I've noticed this with some older Philcos, they will have a multiple code numbers of the same model where they will substitute one tube for another, like a 50L6 for a 50A5. The set you have may have shared it's cabinet and chassis with an AM/FM set, or at least some mechanical parts with an AM/FM set, there isn't really any reason to have vernier tuning on an AA5 at all.
Regards
Arran