As far the CAA is concern if you want to validate your hours as multi crew, you will need a letter from the chief pilot and a copy of the AOC (i.e: no multi crew hours on a private operation).
In Switzerland, you need a multi crew entry (r or l seat)for the 525 on your licence to be able to log the hours.
France is P1 only for both private and commercial.
Each member state have their own way of dealing with single crew ACFT.
But flying private, only one pilot can log the hours and they are all P1.