I think the reason(s) people don't appear, do appear, disappear, reappear, etc. are that sometimes the name is misspelled, making it difficult to locate the person on the index; sometimes they are living in the household of another person and not indexed (although in the later censuses, they are usually often indexed even when in someone else's household); and that sometimes they have indeed left the area, only to return at a later date! Beth BSmith7439@aol.com