Windows Product Key

I would like to know if there is a way to tell what version of Windows XP a product key matches(SP1, SP1a, SP2). I work with a quite a few older HP and Dell systems that need to be restored often and need to know if I can pinpoint what version of XP the product key is for. I want to know what version of XP came pre-installed on the system by just looking at the product key on the Certificate of Authenticity. Any suggestions?