I think you updated to 9.2.1 (13D15) on your phone. The new version, which is only available via iTunes, is 9.2.1 (13D20). It only fix the Error 53 that some people had when they upgraded/restored their phone if it has been repaired outside an Apple Store.
So don't worry, you can just leave it on the 13D15. Or you can upgrade to 13D20 if you want, it's up to you.