Total can of worms:>
The logging of hours when operating a non two crew certified aircraft, by a second crew member is and always has been a can of worms.
Many years ago, I was involved in a PA31 operation, which is basically a sinlgle pilot aircraft. We had two full crew stations, and the private owner wanted two crew, but was not too concerned as to the licence status of the second crew member.
The licences were: P1 had a CAA ATPL, and typed. The right had a PPL, and IMC rating, with twin rating.
The P1 was also conducting AOC flights other than this operation, on different types.
The Co Pilot was allowed to LOG 100%, IF they were in sole manipluation of the control, in "command" of the flight, and no other persons on board.
The approval for this came from the CAA, due to the situation that as a single crew aircraft, the P1 was not a required crew member provided the P2 operated within the restrictions of ther licence.
Thus I as the P1, could be on board the PA31, sitting in a crew station, all day, (but not influencing the conduct of the flight), and then "become" a pilot and operate an AOC flight...
Remember the Pilots Assistant....
SilverS