Getting two different size dimensions front rotors

Ok I went to VIP to get my front rotors and brakes for my 2016 Chevy Impala ltz limited .Now in there computer going by my exact make and model year so on. They kept bringing out rotors that I jus new were to big and nobody could understand why and they tried different brands of rotors and so on with the same result they were to big at this point me and the employees were clueless to why this was happening . So then we decided to put in my vehicle Vin number instead . And sure enough they went to grab that rotor and it turned out to be a smaller dimension. Does anyone have any idea why this would happen . I Kno sometimes they make mistakes but we went over everything top to bottom together on the computer and everything was correct as far as putting in my vehicle info . But the VIN number clearly did something different to get a different size pulled up when putting in all the correct information on my car was coming up with bigger size . If anyone has any answers to this would be very helpful myself and VIP both was at a loss of words with no explanation.

Thanks very much if you could shed any light on the matter !!!