Wouldn't we agree that a swiss only marking would mean radium luminous? Or were the first version 2446 with tritium? Would make no sense to have an early dial with radium marked with the T as in is case. I would assume that if the T is from factory it would also mean that the original lume was tritium?

I'm not familiar with Heuer but that would be the most likely with many other brands.

Cheers