Joy, Someone else posted you a message about the Abercrombie-to-Crombie theory.I agree with his response in part, for I found the same error years ago in the Census.The Abercrombie line I was searching disappeared for about 20 years, then reappeared.I arrived at the same conclusion that: 1. Maybe the census take didn't hear the name and wrote WHAT HE THOUGHT HE heard; 2. Maybe Mr. Abercrombie had a cold, or coughed as he was saying his namae and it got written wrong.
We'll probably never know, but the family which disappeared for 20 years WAS the family which reappeared later because of first name and dates of birth matching.
There IS a CROMBIE line, but I have not searched it.However, personally, I believe it is probably derived from the Abercrombie line in the same manner: through mispronunciation or mis-spelling.