Carole, I have indeed found no mention of the "other" George Pembridge, either as a birth or in a census. But I have Monmouth George's birth certificate, so I am confident in his DoB, while the Porthcawl resident's DoB on the 1939 Register is very clear, so it would be strange if he was the same man.
The man whose death is registered in Bridgend is listed as being 76, which would only fit my George if he died and was registered immediately on New Year's Eve; on the other hand, the Porthcawl resident would have been 74 or 75, so there is clearly some confusion here. I had considered obtaining the Bridgend death certificate, but I am not sure that would confirm his identity anyway - if only death certs included the place of birth!
Gareth