The easiest thing to do is get a picture of another SS from your year and compare, are there SS badges or hood louvers? If there's a motor, how big is it? if you're not convinced look for a build sheet under the seat covering or on the driver's side of the firewall (under the hood) for a metal tag, the numbers and letter can be decoded using a website, maybe even this one and can tell you the build date, paint and interior colors, model and spec sheet on your nova.
OK I have researched and researched this on the 72 Nova. I have come to the conclusion that the 5th digit determines engine size, as in an H is a 350 motor, a K is a 350 Corvette option, (Not sure what that meant unless it was spec'ed out like a corvette motor. There is nothing in the vin or cowl tag to determine if it is an SS or not. Look to see if all the trim is on the car, with the chrome down the sides it would be near impossible to duplicate and make it look good, even for a body man with patience. They all came with P/S P/B Front disk and A/C I am told. And had either a 10 or a 12 bolt differential in it.
The 5th digit of the vin should be a "K". This is the only year that you can tell if it is a true ss without paperwork. The ss did get the higher hp engine compared to the others. The rearend would be an 8.5". The 12 bolt was not available in 72.