When Johnny and Mark save Denny from Chris R., they claim they are taking Chris R. to the police station. However, they re-appear in the scene almost immediately after (within 2 minutes of screentime, which is meant to be in real-time), with their having been obviously nowhere near enough time for them to have taken Chris R. to the police and done the appropriate interviews/paperwork.
Greg Sestero is called Mark as a misguided reference to the actor Matt Damon and his film "The Talented Mr. Ripley." Writer/Director Tommy Wiseau was very taken with the film, and decided to name a character after Damon... however, he misheard "Matt Damon" as "Mark Damon" once during a conversation, and thus wrote the name "Mark" into his script for "The Room" instead of the proper "Matt." He never bothered to change the name to "Matt", thus making his intended reference null-and-void.