During the run of 'The Bob Newhart Show', the number on his office door changed from "715" to "751". His office was still in the same location, and had they moved to a different floor, it would have probably begun with a different number from "7".
I think it's a simple splainin. In order to facilitate faster mail distribution throughout the building, the numbers of each room on the floors were re-assigned. So it was the same office, different numerical designation.
Unfortunately, we don't get the full 'Lost' sequence with that first number - "415", "815", these would have been better for a cosmic link to "the Numbers".