73 Nova SS SDN or Hatchback

Hi I am new to this site and excited to be here. When I was in my teens my dad and I built a 74 nova, we both loved that car. Not long after high school I joined the Army and we decided to sell the car. Almost a year ago today my father passed away, so as a tribute I decided to find and build another nova. In December I found a 73 Nova SS, I first saw it on craigslist with a purchase price then saw it on Ebay so I knew it did not sell on craigslist. The car did not reach the set reserve price on Ebay but I knew from the craigslist add what the woman was looking to get, so I contacted her and offered $500 less than the craigslist add and she accepted. The next day I drove the 300 miles and picked it up. Here’s where my question and concern comes into play. The car is in good shape and runs well but in my excitement and haste I failed to do all of the research that I should have. I checked the title to make sure that the Vin number matched and had her sign a bill of sale, then I was on my way. I am now starting to work on the car and gather info, from every site that I have found about VIN decoding the third and fourth number in the VIN determine if it is a sedan or hatch back. If it is a hatchback the number is a 17 if it is a sedan it is a 27. The VIN on this car has 17 as the two numbers depicting it as a hatchback but this car is clearly a sedan, how can this be? Any help would be greatly appreciated