Written by;
Karl Neiswender of A. A. Best co,
User ID best-man
40 years in the business, 39 years hands on installing.

Convertible tops have two basic rear window configurations.
Some have the window built into the top and some have a separate window.
Those with the window built into the top are in the minority. They include Alfa Romeo, Austin Healey, BMW, some Camaros, Capri, Corvette, 05 and newer Mustangs, Triumph and more, mostly European cars.

The vast majority of American cars since the 40s were made with a separate window unit.
To one who has never installed a convertible top, they often look like one piece because they are fastened to the car at the same places.
In actuality the window unit is fastened to the car and folding frame, then the top is fastened over the window. This becomes obvious when you realize that on these cars, one can actually reach into the car by going under the top at the side of the rear window. 
The rear window unit consists of a glass or vinyl window surrounded by the same fabric or vinyl that the top is made from.

With this configuration, one has the option of replacing a top only, or a window only.