They were electrically different, depending on the field coil requirements of the particular chassis. For example, those used on a 12 tube push-pull chassis used a speaker with a lower field coil resistance than those used on the 9-toobers. The beehives themselves were identical for the 9 and 12 tube models AFAIK, but the beehives for the 15-toobers had a bigger cut-out on the inside to accommodate the larger output transformer on the speaker. You could probably use a 15-tube beehive with any speaker, but you couldn't use a 9 or 12 tube beehive on a 15-tube speaker.
Heres the number on the bee hive speaker S5604 K. How do I find whichZeniths used this part #?