I've noticed Roz entering the scene before she should on more than one occasion.

In season 2: Look Before You Leap.
Roz asks if Gary is listening on the show because they had met earlier that day on the bus and before she could give her phone number to him, they were separated. When Gary shows up at the studio, Roz finds out he's married and chases him up and down the hallway, beating him with the very flowers that he had bought for her. Near the end of this scene, Roz had chased him into the room behind the room Frasier does his show from. As Frasier is ending the scene, Roz can be scene coming to the door way, but waiting for the scene to end.

In Season 5: Halloween.
This is the scene where Roz may be pregnant and goes to one of Niles' back rooms while his Halloween party is taking place. The cat is out of the bag when Niles mistakenly thinks Daphne is pregnant with Frasier's child. When Frasier straightens things out, Roz comes walking out of the back room. Seconds later, Roz comes walking out of the back room again to announce she is pregnant.