Your right, I should mention that we would call safety pilot, supernumerary - which is as good as useless to you in terms of PIC, dual, totals etc.
Case M basically describes you taking a passenger on your existing licence (i.e exactly the same as case A)which of course you log as PIC, but the 'passenger' would have to log it as supernumerary which again is practically useless.
Also I've never ever met anyone who actually logged the supernumerary.