Forgive the slight diversion, but the much missed Coffman Starter partly answered the question about PMK here in 2013. - Archimedes
Much obliged Archimedes, both to you and the greatly missed Coff in absentia, for the enlightenment. Interesting to note that HRH Prince Michael was barely out of Sandhurst at the time, aged 20, and that he is not shown in Army Lists as either "pl" or "ph", which does indeed seem to suggest a less than full course of Service flying training.
By contrast, I'm quite taken by the fact that HRH The Duke of Cambridge resolutely only wears RAF wings when in either RAF or Army uniform, but never
AFAIK in naval uniform when worn after becoming fully qualified on a shared type of aircraft.
Jack