Serial numbering on our various products is not uniform from model to model. There are several reasons for this, and has to do with our production schedules, build dates, and other internal matters - nothing to do with quality control or pair matching. Some of our models use sequential numbers and other models use the same number, but with a L and R at the end of the number. In fact, we often interchange this sequence within the same model, for reasons I won't go into since it isn't anything terribly interesting to an end user, but I can say that sometimes a R speaker is built one day and the L speaker is built on the following day. Part of our numbering system represents a "date code" so in essence, it is simply a tool for us to keep track of what we're building and shipping.
By the way, we don't use pair matching, it's a band-aid to enable a manufacturer to use drivers that don't match and then correct for the mismatch with the crossovers. Instead, we build to a "golden unit" which every speaker must pass. There is only one reference speaker in our lab and computer files, and all speakers built must track that reference unit or it gets rejected. Since we test each part before assembly, nothing gets rejected after the speakers are built, the parts are rejected during the component test phase. Since we're using Grade-A drivers in the VR-5 Anniversary, we have found very few defective or out-of-spec drivers. Although years ago we tried "pair matching," it was far too difficult and expensive to build each crossover for each drive unit, so I asked the driver manufacturers to send me only Grade-A drivers that all meet my personal requirements. These companies are very happy to accommodate this request. This greatly simplifies the repair or replacement of a speaker out in the field that requires servicing.
