Build 7600 was compiled twice with the build strings:
7600.16384.090710-1945 and
7600.16385.090713-1255
with 7600.16385.090713-1255 being the gold code, RTM, final, retail, what ever you want to call it. Assuming this is the build you are using, which unless you have followed the whole build process, Im sure you will have. You will not need to upgrade. I assure you Microsoft will not change the code for retail. Infact, the disks will have been stamped and probably in the process of being shipped to your local store.
If you have have this build, and you have it legitimately, you should have no problems with expiration as you should also have a product key.