In my experience all companies and militaries have differing policies on this issue.
If you are qualified as 1st Pilot on type, then you can log all flying as such...but you cannot log it as PIC (assuming your national logbook has seperate columns for it.
2nd pilot time is really only time your hands are not on the controls...as such it adds to your TT, but otherwise is worthless.
In short, if you have a rating log 1st pilot.
Some S76's are only registered as 2 pilot IFR. Therefore, off-shore, or when anticipating that part of the flight may be conducted IFR, then 2 pilots are required..if not you're by yourself.
I appreciate your question...as I said a every outfit Ive seen does it sligtly differently.....2nd pilot in an R22; you're pulling my leg!!