I have watched Newhart over and over(the whole series), and I can't believe I never noticed this little mistake from Joanna.
It is during the 3rd episode, when Joanna is introducing Mrs. Wannamaker to Dick, she says, "Dick, this is Mrs. Wannamaker from the Welcome basket..." She of course meant to say, "Welcome Wagon."
I just watched this episode last night, and it blew me away that I never noticed it before.

I also wonder why they didn't redo that scene. I guess they missed it too.

I've wondered about these kinds of things on other sitcoms. I think you hit it: the director (or dialog coach, if there is one) just didn't notice it.

Yeah just one of those little things that slipped by them LOL.

Ed.