I'm a bit late to this but the markings are similar to an example I have. Pretty much standard proof and inspection marks, The RAF stamp can be a bit misleading as some pistols were given this stamp but not necessarily issued to them. Pistols of this type were a private purchase item. I agree that the '13' stamp is probably a rack number, and I wouldn't worry too much about the quality of the stamp as these were often done in the field prior to being issued out. I attach a photo of mine for interest.