It's that rare nowadays?
I'm inclined to agree with Thoreldan; PFC was also less of a pure
promotion & more of an "appointmental " rank in my time. In my
case, it was the Arty detachment layers who were - rather quickly -
advanced thus, to distinguish them from the rest of the mortarmen
(who remained PTE's).
Ultimately, though, there's no permanent distinction since the bulk
of the mono-intake conscripts would collectively make LCP before
they ORD, & that's the highest rank they could climb to.