There's also PRG: which is equivalent to PRG0:.
Note that there are actually only 2 file types, and all these names are just for telling SB how to load the file.
All of these:
PRG:NAME PRG0:NAME PRG1:NAME PRG2:NAME PRG3:NAME TXT:NAMErefer to the same file (Internally, this is saved as "TNAME"), and
GRP0:NAME GRP1:NAME ... GRPF:NAME DAT:NAMEall refer to another file (saved as "BNAME")