I've been looking at 1940 census and was reminded that one should always make certain to analyze every tick mark and notation on the census (or any record for that matter). Some abbreviations on the census are statistical and have nothing to really do with the family's entry specifically. Other items can be clues. Marriage and other records can contain small clues as well. The marriage register may list your ancestor as Sally Jones and the marriage license may list her as "Mrs. Sally Jones."
And that's a big difference.