There's always the HELP file. I know for a fact, that the counter and UDC is listed in the help file.
C (or CTR) is for counter and the number range will depend on which keyence you have. If you download the manual, it also gives examples for usage and tips for using different relays to reset counter on first scan, etc.....
There is also an up/down counter with an 8 digit bcd output, again the address will vary.
v_kv_pro_ch02b.pdf. I think it was part of a larger zipped file but can't remember back that far.