1973 K5 with a fuel door??

[63longfleet]

My son just brought home a 1973 K5 he picked up today. It didnt have a title just a bill of sale so cant verify year there. Here is my problem it has a fuel door like the later models and not the exposed cap on the side of the bed. I checked the vin "cky183f163164" and as near as i can tell it showes to be a 1973 Blazer. Did some trim option come with the door instead of the exposed cap or what.