Searching the forum (using google) -

https://www.yamahasynth.com/ask-a-question/confusing-waveform-naming-convention

These other ones are up to debate. If I were to guess, I'd say they were abbreviations for trademarked stuff that shouldn't be spelled out in a Yamaha manual.

Maybe ZJ = Zildjian they make and brand lots of drum stuff. Mostly known for round frisbee things that make different lengths and kinds of racket when hit.
Maybe LW = Ludwig
Maybe TM = Tama?
Maybe CP = Pearl CP?
Maybe PT = Paiste?
I'm getting fuzzier and fuzzier - guessing more wildly.
DG = David Garibaldi? This is a departure since these are Yamaha signature snares. So presumably it'd be OK to show more of the cards here. Could very well be off the mark
AT = ?? I have a guess that's even more far fetched than the previous.

Got a less far fetched guess for "AT" (one I'll at least make public) - but still pretty far out there. Enough to still be last in the list (they're in order).

AT = Arbiter AT?

- What is the meaning of suffixes like "St" or "Sw"?

St = Stereo
Sw = (velocity) Switching

Waveforms can be as many as 256 samples... so a single piano Waveform could itself be a multiple velocity switching entity
A single string Waveform could be the entire orchestra sampled in Stereo.

- Sometimes I find at the end 1-2, 1-3 or 1-4?

The number ranges give you the number of velocity switches. For example, if you see a snare or HH with 1-4 after the name it signifies that there are for samples stacked—each triggered at a different velocity. Try them, you’ll discover that this is the case... you’ll hear timbre change as you increase velocity applied.

A Waveform is a collection of samples - they can be laid out horizontally and/or vertically. Drum Kits, by definition occupy a single Key so the samples are varied vertically (by velocity range).

The guesses at the capital letters as outlined by Jason are as good as any! Whether they are correct or not, I don’t know.

They identify the different drum/percussion samples for the programmer... maybe we can find out from the original programmer what they stand for... but much like any of the listed Waveforms, Arpeggios, Performances, etc., you really have to play them (audition) them to know anything about what they sound like.

On some of the Factory Performances a programmer’s initials made it through to the name... some have a programmer’s daughter’s name... so perhaps they are people, perhaps they are signature drums, etc. The fact is, regardless of the actual meaning, you still have to audition it to know what it sounds like. I think that is why not much emphasis is placed on such things.

Thanks for this information, and also for Jason's additional link. Makes sense to me, case closed.