21215+ have all had the Timebomb code and everything removed from them.
HTC has been making roms from 6.5 for a while now. I have some HTC SYS from 21189, 21193, 21194, 21202, 21210, and a few others. from anything from QVGA to WVGA, so HTC has had the files for a while.
HTC when they release the files will be 216xx,
The MS files are all 212xx, and the OEM will then change the build number and add there own fixes to the sys and everything from there. It seems like Samsung has the 215xx, HTC has the 216xx, and that is all I really know for sure at this time.
HTC is testing just MS builds at this time then 212xx, and I have only seen a few HTC release roms at this time. one 21602, it is a higher number but it is based off 21215 area, it is not a fake build, it is just a higher number to deal some things that HTC fixed.
Da_G seems to know more about this then I do, but here is something that he posted.
http://forum.xda-developers.com/show...postcount=5048