In the 1940 census, I could not locate my relatives where I knew they had to be. I had their correct address from a 1940 city directory, so I knew they lived at 4444 River Rd. I had the correct ED and block number, so excitedly I find 4439 River Rd., then 4440, 4442, and then the enumerator went on to the next block, skipping 4444 and 4446! Agh! Disappointedly, I asked my mother (who used to work for the Census Bureau) what their instructions would have been if they realized that something had been skipped. She said to look at the last page of the ED and see if the missed addresses were added there. They were!
I just thought I would share this since it seems this seems to have been a fairly common occurrence.