The glass rear window was introduced in 2002. All earlier cars (97-2001) had plastic rear windows.
And yes, the plastic windows folded when the top was opened. Some owners would even get out and manually "chop" the middle of the plastic window to help it fold nicely when opening the top.
Read all about the "chop" here:
Automatic top chop?
Many 97-2001 cars have had the original plastic window top replaced with a glass window so its pretty common to find the glass rear window on earlier cars.