Well, the last actual "seeded" build was 10A380, given in disc form at WWDC--there have since been 4 kernel updates to that build distributed online via software update. In the latest, 10A421a, the kernel is officially final (10.0.0), so I am betting that there won't be many more 'update' seeds (if any). All subsequent changes will be minute, mainly consisting of bugfixes to kernel-mode drivers that need to be reworked for the pure native x64 version of the OS.