SIC and PIC time is given fractional credit for currency, IOE, etc requirements. Two pilots = 100% each. Three pilots = 67%, four pilots = 50%. We actually could contact dispatch to give the real breakdown of seat time if we wanted. That was typically only done on IOE's when the actual seat time might matter. I'd take shorter breaks but we never bothered contacting dispatch to reduce the percentage of time the others actually sat in the seat. There's nothing, in the U.S., I've seen that talks about not logging all of the actual flight time. However PIC time does switch over if a second PIC takes over command. A relief Captain sitting in the seat while the Captain is on break is not the PIC. The real Captain could actually assign the FO to be the 'acting PIC' while he is on break instead of the relief Captain. Some companies do a mid flight change of command. At that time the PIC stops for one Captain and transfers to the other Captain. If that should occur on a regular flight we'd notify dispatch that Captain XYZ is now in command. About the only circumstances would be pilot incapacitation OR removal of the Captain by a management pilot/CKA while in flight.