97.5 or 98 Regal GS any differences?

Mine is 97.5 GS. An oddball year. Sometimes when i get parts, i am given the wrong part, and the computer at the autostore says part is for a 97 Regal but it is still the wrong part. When i ask for a 98 Regal GS part i always get the right part. This has happened at a few different auto stores, even the dealer too. When i give the VIN, only then will i get the right part. Was there a 96 or 97 Regal GS? I know mine is 97.5. One of the books from the dealer stated it. And on the door or trunk i seen a production date. I think maybe august or september. If anyone knows why this Regal is 97.5, please tell. And....will it help keep its rareness and value like the Mustang !/2 year car. I think it was 67.5 or 65.5