I decided to revisit this thread with another observation:

It's true that not everybody in America drives a new or newer car. When I first got interested in cars in the late '50's in NYC, there were plenty of early '50's and late '40's cars on the road. BUT, careful directors like to use the most current cars for the period to lend authenticity to their scenes. For example, when Michael's in Florida with Roth in late '58, he's driving a '58 Ford Custom 500--exactly what "Mr. Avis" would have rented to him. Johnny Ola is driving a '58 Chrysler New Yorker. Michael's driver in Havana has a '57 Mercury Montclair.

Even more authentically: at Connie's wedding, you see a great variety of late '30's and early '40's cars because it would be credible for guests to drive a variety of cars. Also, no cars were built in the US during the war years.

One interesting exception: Carlo is garrotted in a '51 Plymouth Cranbrook in 1955, even though most of the other cars in that scene are '55's. Why would Clemenza take Carlo for his last ride in such a cheapo? Because, for drama and authenticity, Carlo kicks out the windshield--and the windshield is made of "safety glass" that doesn't shatter on impact. All US cars had to have safety glass since the '20's. My guess is that they used that old Plymouth because they bought it at a junkyard, and just dumped it afterward--replacing the safety glass would have cost more than the car was worth in '72.

By contrast: early in "Goodfellas," young Henry Hill, working for Tuddy, smashes in the rear windows of cars parked in lots, pours gasoline in the cars and sets them on fire. Notice that the glass shatters. That's because it's "movie glass," made out of spun sugar. Probably they rented the cars from an agency that supplies vintage models for movie sets, removed the safety glass rear windows, substituted movie glass, and put the original glass back after they shot the scene.