3) "from the moment when, after the embarkation of its crew"..... So have we had a crew member logging P1 when he was not actually in the aircraft?? Co-pilot start-up taxis out, Captain joins him at the threshold.
Ah, no. The co-pilot logs P1 for the taxi bit. You can hardly be "in command" if you're not in the aircraft, can you (unless it's a pilotless, radio-controlled aircraft)?
Question is, during that taxi bit, was the co-pilot PF or PNF?
Personally, I've been involved in another interesting scenario. Taxiing out for my first solo and the aircraft failing its runup checks at the hold, so taxi back to the school to had the engineers take a look. I had moved the aircraft with the intention of taking off, so legal to log P1. My second first solo actually got me into the air (and safely down).
There's also a bunch of interesting scenarios where the pilot hand-swings the prop but forgot the chocks or brakes so the aircraft starts taxiing, or even taking off, on its own. How do you log that?