by the looks of your info offered your car may be one of the exceptions to the rule of thumb, like your assembly was held out of line for one reason or the other.
it is more than likely that your car was finished and inspected sometime after the updated change for the FMVSS decal for the following month and that's just an opinion on the limited info you provided. however not sure there is anymore info to provide about those dates unless as they "now for the rest of the story".