My SSK (IIRC) had it's keys replaced by new Unicomp ones by the previous owner. Unfortunately, the printing on the batch he got wasn't great, and they look like they are worn. Ironically, I ended up swapping some keycaps from a Model M from 1993.
If I look really closely at the printing on my Model F, it's not completely consistent. Hard to know whether this was the way it was printed, or whether it was some degree of wear.