These are people who are living in London but aren't born in London, and for whom I have no current information tying them to a place. This is only the case for 1841 census where the question was only whether you were born in the county where you were living.
1841 Census Middlesex St Andrew Holborn
Richard Dickins 30 Chemist
Mary Dickins 20
Charlotte Dickins 2 months born Middlesex
Only baby born in Middlesex