The reason Bruce Willis is not credited is because he violated SAG rules for acting in this film for no money. He appeared for fun and as a favor to Quentin Tarantino, and acting for free violated SAG rules. SAG agreed not to sue Willis if his name was not included in the credits.
Quentin Tarantino's "A Band Apart" Production logo at the beginning of the film shows 'Tim Roth''s "Mr. Orange" unzipping (shedding) his character from Reservoir Dogs (1992) and becoming the bell hop character for Four Rooms.
Just before Ted answers a call from The Man in "The Misbehavers", a package of Red Apple cigarettes is visible near the switchboard. This fictitious brand of cigarettes features in other Quentin Tarantino films.
Lawrence Bender, who has produced and founded the film production company 'A Band Apart' with Quentin Tarantino, appeared in the segment 'The Wrong Man' and was credited at the end of the film as 'Long Hair Yuppie Scum'. This is the title that he was credited with in Pulp Fiction (1994).
When Ted first enters the Penthouse suite (when Angela says "The Bellboy's here"), the camera goes all around the suite to introduce Ted (and we, the audience) to Chester, Angela, Leo and Norman. It also continues through Chester's praise of Cristal and Jerry Lewis, his temper tantrum, and his self-congratulations about the success of his movie, ending with Norman lighting Angela's cigarette. All in a single take.