The actual law says, "Energy Star most efficient certification requirements."
https://www.law.cornell.edu/uscode/text/26/25C
Anything in the instructions can only be an aid to following the law (and there have been rare occasions where the instructions didn't follow the law). Although I would suspect that if the instructions give specific efficiency ratings depending on climate zone, they were probably copied from the Energy Star web site. I would check the Energy Star web site for the ratings that were in effect when you installed the windows and check with the manufacturer if you are not sure.
