Danny
A very good summation.
It was exactly same same here in Oz. I guess you would expect that as the RAF was modelled off the RAAF. Or was it the other way around? Always get confused on that !
Also after WWII our NCO aircrew went briefly through that similar P1, P2, P3, P4 debacle. By about 1960, all pilots and navs commissioned.
(Sigs a little later in the mid 60s, when they became AEOs - which was subsequently switched back to NCO AEAs.)