I was blog surfing today and found something interesting on another blog. The blogger asked his readers to identify 2 cars in a picture that he posted. One of the cars is a Chevrolet Impala. The other car, well, there's a bit of a disagreement as to it's year.
To end this, I'll post pictures of my first car. I was 19, back in early 1980, when I purchased a 1973 Buick Riviera. The Rivieras built from 1971-1973 were the only boat-tailed ones. Earlier year Rivieras, such as those from '66-'70, had a fast-back with the long, slanted, rear window glass, but '71-'73 were the only ones to have the tapering, curved, rear glass of the boat-tail. The rear license plate on the 71s and 72's was mounted left of center. On the '73's it was center mounted. The grills were different on '71 and '72's, they were a bit more under-cut and sharper than the '73's. The '73 grills were a bit more vetical than the '71 and '72s. 1973 front bumpers were larger and heavier looking.
Gary, I hope this clears it up...
Gary, for even more information on Rivieras, there's always Wikipedia for Buick Riviera.
Edited 12-20-11 to add better pictures!