Sherlock Holmes Fic Finding Community

I have always had the impression that 221A was some sort of shop, and 221B was the residence beside/above it. At any rate, Holmes was living on Montague Street "...when I first came up to London..." (The Musgrave Ritual). There is no mention of a residence other than Montague Street, Baker Street, and Sussex (except a fleeting reference to being at university).