The letters A, B and C are waveforms variatios of the same sample. When the sample itself is a major sound change, you have a number (like Organ 1, Organ 2, organ 3...).
p, mf and f are pianos
p= piano
mf= mezzoforte
f= forte
This info is in a Roland S700 Sample Library; Roland uses the same naming convention in the JV/XP synths and expansion boards.
Also Roland refers to synths of others makers as abbreviations
MG = Moog
KG = Korg
P5 = Prophet 5
OB = Oberheim
OBXP = Oberheim Xpander
One exception:
JP-6 and JP-8 are Jupiters, but Roland has a copyright issue on the name...
Mgomes