I just watched the episode where Roger becomes the Principal of Patton High School, and when the kids chase him back to the Cunningham's house, Howard comes in carrying their mailbox (conveniently ripped off by one of the rowdier students). Contrary to the familiar 565 we are used to seeing on the front of the house when they come back from commercial breaks, the mailbox clearly
displays:

Cunningham
4265 Jefferson Ave.

weird, huh?

Good eye, Roby. I never noticed that one.

That's yet another inconsistency with the Cunningham Address.

The Cunninghams had at least 2 addresses. One was 565, but I can't remember the name of the street, the second was 179 Bridge street. In the episode "my favorite orkkian" in which Mork in street clothes disappears, we see the house number.