The term matched pair of mics means different things to different people, including the folks who make them. Some manufacturers maintain that any mic they produce of a given model sounds so much like — or “specs” so closely to — others of that model there is no reason to specify matched pairs; essentially, they claim that any two of the mics constitute a match. Other manufacturers offer, often for an additional price, to put their mics through extra testing and then pair those (typically in a single box) that sound the most alike and have the closest specs. Still others offer matched pairs with consecutive serial numbers, the idea being, perhaps, that two mics made immediately one after the other (or at the same time) offer a greater likelihood of being sonically matched as well.
I've tested many mics in recent years, and there were sometimes clearly audible differences between two mics of the same model, whether dynamic or condenser. (For the few ribbon mics I've tested, this was not the case.) Therefore, for critical stereo applications, I prefer pairs that are sonically matched. As for consecutive serial numbers, that seems to me more a cosmetic concern.