The engravings on the inner side of the case back (obviously, the case back has to be unscrewed for you to see them) can confirm most of the information you gathered from the previous step. Here you'll find the reference number and the production year of the watch, albeit those might vary slightly from what's on the case. Sometimes you will see a slight difference between the two; this is okay as long as the references are substantially identical in build. For instance a Submariner No Date 5513 with a 5512 inside the case back doesn't mean the watch is incorrect; the only difference between those two watches came from the Chronometer Certificate for the latter. Similarly, the dates don’t have to overlap perfectly, as some parts were put on the side during the manufacturing process and would only be fitted a couple of months later, with a newly produced case. I would nonetheless consider any discrepancy over one year or so as suspicious, at least for the most successful models, which obviously could boast of a high degree of rotation in the inventory of the ADs. Of course, being able to read the engravings on the inside of the case back implies that the watch was properly opened by the seller; in that case the movement will also be a precious indicator, from the shape of the rotor to the engravings on the main plate and the bridges.

One last thing about the case back that does not even require prior opening: checking the outer side allows you to confirm the back was always opened with proper Rolex tools. Otherwise signs of a forced opening will be present – usually in the form of either long scratches or deep dings. Such ill-advised attempts to force open the case back, aside from producing cosmetic damage, can actually warp the case back enough to compromise the water resistance of the watch (and if someone has been foolish enough to try to open a Rolex case without the proper tools, they may have left other unwanted calling cards both inside and outside the watch, so be extra careful).