What exactly is the difference between the SPXX and the SPXXX series?

EBF 21517: 15.7 SP102 - 64 Bit 15.726 Jul 2013EBF/Patch






EBF 21202: 15.7 SP50 - 64 Bit 15.723 Jul 2013EBF/Patch

Why is there are SPXX (5x and soon 6x) and a SPXXX (10x) series of ebfs? There doesn't seem to be a clear indication. I'm leaning towards the idea of whomever thought that numbering scheme up was up to something devious