I have an 83 280ZX I bought new in Oct of 1983. My VIN ID Tag says the date it was made was July 1983 (7/83) and the serial number is over 580000 ?

According to the Vin Number & Serial Number data on the internet and another Z Club sites the car was only made between 7/82 - 6/83 and the serial numbers run from 550006 to 575494 ?

Can anybody help me get more info or suggest who to talk to. I've talked with Nissan USA and they only info back to 1985.

Thanks.
Terry Sweeney