City directories are awesome. Before 1940/50 census I was able to follow surnames all thru the city. I found male surnames. It is difficult to keep up with the ladies. A lot of families tried to live close together. When times were really tuff, they would stay in the same housing. Then you would see different surnames at the same address. That's when I would make note of it and and follow those names.
My I loved when they would segregate names with the (c) for colored made it easier to know who was who. Later if it was dropped you could tell what jobs were held by what people. Ancestry called it the substitute census. I called it--the 'thank you directory'.
I was also able to figure out when a uncle died, He was always listed as head of household and his mother was in the household just as (Lucy). Then one year it was just Lucy at the same address. No one in the family could remember when he died and there was no accurate death certificate. Found it for that year.