I used to work on this project for the Census Bureau back in the day.
There is no “pattern” as to what is verified and what is not—any neighborhood or country road could have a new mother in law apartment, trailer etc added...regardless of local laws, ordinances, or covenants.
I worked on the 1990 census from summer 88 through fall 1990. It was terrific for me. We were remapping everything and verifying addresses, etc. I had been working catch as catch can and this job got me caught up on everything. I worked very fast compared to the college students and retirees who were most of the rest and I did it on a 55 mpg motorcycle while getting the same mileage money as the old guy in the Cadillac. Come the count itself, again I worked far faster than the others and when bonuses started being offered because it was dragging so badly I got the max bonuses possible. I could do a hundred addresses in the time that it took Joe College to do 6. Finally I was put in the ghetto sections of Tallahassee and Fort Walton to clean up the areas that everyone else was afraid to enter and then I was put up in a hotel for a week to work the phones to prod offices all over the state to get their asses in gear and to confirm items that had questions. I was sorry to see it all end. When it did I went fishing (commercial, that is.)