Funny fact, though. By the time the movie came out the YB-49 had already been grounded.
One more movie that has the YB-49 is "The Incredible Mr Limpet" (1964). When Henry Limpet imagines (as a fish) how famous he will be, we see a shot of a YB-49 flying over that transforms into a manta ray (in animation). Set in 1944, the YB-49 had not flown yet, but a cool shot none-the-less.