Reversebucket,
Clearly these are examples of low hanging fruit in which the capacity of the logbook holder is signalled by the signature of the instructor.
Ambiguity may continue to exist for flights involving a required safety pilot and in which neither pilot holds, or exercises, a flight instructor certificate. In genuine cases free of misrepresentation it would be absurd if one of the required pilots could not log pilot-in-command for EASA purposes.
Meikleour,
Surprisingly, this test can fail to produce the desired outcome in the US. The Office of the Chief Counsel for FAA has provided an opinion on this in the
Speranza interpretation 2009.