Do pilots get full credit hours when they fly double or augmented?
It really depends on the individual Air Regulations of each country, and the union contracts of each airline. Pilot union contracts are often more restrictive than the Air Regs of the country they operate in. 

In my experience, North American airlines with "formula pay", both sets of pilots log the entire flight, because they are paid for the entire flight, even when they are sleeping in the bunk. 

Other airlines who pay monthly salaries, with bonuses for extra overtime hours, do not credit the pilot for time in the bunk, and they tend not to log those hours either.