Continuity mistake: In the office Kaufman's agent tells him that he has a gig with a major network - he doesn't say what network - yet Kaufman tells Danny DeVito that ABC has give him what he wants.
Revealing mistake: When young Andy Kauffman is performing the "Animal Song" for his sister, he mouths the words "Meow meow" along with her. Although one could argue that he was expecting her to say that, how would he know she was going to say the word "meow" twice?
Factual error: In the film, Andy plans the Carnegie Hall gig after learning he has cancer. The actual concert took place in 1979, when Kaufman's popularity was at its highest, not near the end of his life and career (1983-84). (Regardless of the writers' intent when writing the script for this film, it is still a factual error.)
Factual error: In the movie when Andy reads the paper saying he got voted off Saturday Night Live, he remarks "This is bad, I only got 28%." In reality the poll was much closer, with about 46% voting to keep him vs. 54% to dump.
Factual error: David Letterman didn't wear glasses on TV in the early '80s.
Factual error: On the set of Taxi when Tony Clifton is fired, which took place around 1978, one of the chopped vehicles shown on the set is a mid-1990s Chevy Caprice.
Factual error: Andy didn't meet his girlfriend Lynn when he was wrestling women on the Merv Griffin show. They actually met in 1981-82, when his "wrestling career" was dying down (incidentally, if you rent the movie "My Breakfast With Blassie", you actually see Andy meeting, and hitting on, Lynn for the first time. They had never met prior to the filming of their improvised scene. It's pretty funny-rent it!)
Answer: We're supposed to wonder if Andy didn't really fake his own death.
Xofer