I think you have to consider the context in which Fleming wrote those early Bond novels. For 1 thing, Fleming, himself, wore an Explorer & as is still the case today, most gen owners no little about Rolex watches beyond what they see on their own wrist. So having Fleming make note of the luminescent glow & 'Oyster Perpetual' markings on Bond's Rolex would seem quite reasonable when describing a character wearing an Explorer. After all, Fleming would need only to look down at his own wrist for inspiration. Secondly, if Bond's watch had been a Sub, I find it difficult to believe that he would mention the dial's inscriptions & luminescent glow without noting the bezel's rotating nature, which, at the time the early Bond novels were written, (1950s) was a very unique & notable feature on a wrist watch. It is just very difficult to believe that Fleming would describe Bond wearing 1 of the then-new Subs without mentioning the watch's unique bezel, especially in view of how it would have required 007 to reset it (back to null) after having used the watch as a knuckleduster.