You are right to be cautious about adding all in a census. Many, many times between one decade and the next, a different name may be used. For example the name Elizabeth. One census might record her as Elizabeth and the next decade she may be Lizzie and the next Lizzy and still another she may have married and a different surname is recorded. If a person is not careful, 3 profiles for the same person could be created just using this census option all 4 times. I do believe that is exactly what happens with some trees. My opinion: use the census to record one person at a time. It will take longer but in the long run will be much safer.