AS to the watches results not resembling the performance noted on the certificate...that is probably why Rolex stopped issuing the individual certificates with their watches ha ha! :-) My Explorer II when I had it actually began to run a couple of seconds faster after I had had it a while...I was extremely depressed because it had been like + 1/2 second per day and then it went to about 3 seconds...You love it when you get one that you just never have to set and mine started out that way. Though newer style movements with quicker beat and better over all design are much more stable than their predecessors, the timing is still affected by a persons wearing habits. If you play tennis for example, in your watch it will likely run faster than if you don't. Not that I recommend that ha ha! I just remember my watchmaker telling me the story of a gentleman whose Rolex he serviced complaining that it would be incredibly accurate and then all of a sudden be several seconds fast. They finally, with a little detective work, figured out that the watch was always fast the day after he had played tennis. The watches of very active people will have a tendency to run a little faster than ones worn by people who are more sedentary. Hans Wilsdorf actually wanted to develop the automatic mechanism because of improved accuracy rather than convenience. The automatic keeps the mainspring pressure more constant. All movements run faster when the mainspring is fully wound and slower as it unwinds, so ideally a watch fully wound at all times would be easier to regulate and offer a more accurate reading. Also how you store the watch may alter its performance slightly. In the old Rolex instruction books, one was instructed to place the watch on its side overnight while sleeping to slow it down slightly. It was also suggested that the watch be left flat on its back if it was running slightly slow, to speed it up. This is gravity working on the pivots of the balance.
You might just have to have the regulation adjusted to make it better.