Hobbit, there is a definitive answer, just look at LASORS it is very clearly laid down in there.
For the seven hundredth time.
P/UT- any time you fly with an FI who logs the flight as P1.
P1/S- ONLY when you fly with an examiner on a successful flight test. A checkout doesn't count.
P1- When you are PIC.
There can only be one P1 logged on a single flight, why does it matter anyway? You may aswell do it properly.