Differences between model year 71, 72 and 73.
The 71 Riviera was a major restyling compared to the 1970 model year. For the year 1972 there were only minor changes but for 1973 there were bigger changes. Here you can find out what these changes exactly are.
Front section differences
1971
You can recognize a 71 at the following specifics: horizontal lines in the grille; small plate holder under the bumper.
1972
Slightly restyled front: New eggcrate grille, front bumper moulding, vinyl body side moulding. This car has the for 1972 optional front bumper guards.
1973
Along with other regular sized Buicks, the Riviera had a new front and rear treatment with new hood, fenders, grille and lights. The 5-mile bumpers with shock-absorbers were introduced and the license plate was moved to the right.
Rear section differences
1971
The 'boattail' was significant on the 71 and 72. Too bad that it lasted for only two years.
On the 71 there were louvers on the deck lid. The taillights had horizontal and vertical lines.
1972
Still a boattailed end for 1972 but the louvres were gone. Side body mouldings were added (also rubber moulding on rear bumper) and the taillights had no lines in them as the 71 did.
Note the Riviera logo in the center of the trunk lid that served as lock housing on the 71 / 72.
1973
Lee Mays almost had it done. The boattailled end was sized down to the window section.
The rear bumper showed just a little sculpture and the license plate was moved to the center.
"The rear glass (or "backlight" as it is properly called) was, indeed, a very difficult part to make. "
- Houlihan