Yes it is the credit hours that count for the yearly limit.
You only log the time at the controls, so on a 4 crew flight of 12 hours you would log about 5 1/2 hours as P2X. Say one hour is when the operating FO and CN are doing the T/O and LDG and the rest is split 50/50 so each pilot gets the same rest.
On most 3 crew flights of say 10 hours you would log 6 hours of P2X, one hour for FO and CN to do T/O and LDG then the rest split three ways so each pilot is getting 3 hours in the bunk or business class seat.
On some 3 crew flight you as an SO are burnt out meaning that for the FO and CN to not exceed the duty limit you have to work so they can rest. BKK to KHI and back is say 5 hours each way, you work for 4 hours each sector, FO rests on the way there, CN rests on the way back.