Is there a difference between the Audi 80 and Audi 90 transmission systems?

I'm in the process of purchasing a used Audi 80 and I've noticed that some models have a 3-speed transmission while others have a 4-speed. Is there a functional difference between the two systems or is it just a cosmetic change?

Yes, there is a difference between the two transmission systems. The 3-speed transmission is primarily found in earlier models while the 4-speed was introduced in later models.