I've read numerous times that watches from the late nineties onwards won't gain a nice patina on the indices as superluminova remains white, even after a number of years. However, just browsing on eBay recently I've seen a few mid-late nineties seamasters, that from the lack of a T on the dial and the production date I assume are superluminova rather than tritium, and these seem to be developing a yellow hint. Is the early luminova different to what is used now? IMO it does I've the dial a bit more character although it's not as nice as tritium. Ive be had to pinch the photo from Google
There are some that go very darkish brown, one of our members recently oven-baked a speedmaster luminova dial too which sent the lume a coffee brown colour
I'm guessing if it wasn't tritium it was a preluminova substance. It is certainlŷ ageing like tritium though. If it looks like a horse and sounds like a horse, it's tritium. Just checked and it is tritium up to 97 so the sm300 probably has it.