[Arran]

 I've seen sets with the tube numbers engraved on the sockets on occasion, usually on sets using older style tubes with fat pins, in fact it's very common in the earlier AC radios, like to prevent people from putting a #26 tube in a #71A socket since both are four pin types running on different filament voltages. But after 2.5 volt tubes became common this was less of an issue since everything but the rectifier was the same voltage.
Regards
Arran