Apple today seeded build 12D74 of OS X Mountain Lion to developers, marking the eleventh beta iteration of the newest version of Mountain Lion. 10.8.3 was first seeded to developers in November of 2012.
This post originally referred to Build 12D74 as the twelfth developer seed of OS X 10.8.3 when it was actually the eleventh seed.
Article Link: Apple Seeds Build 12D74 of OS X Beta 10.8.3 to Developers