Especially as notwithstanding all the tourist nonsense and most screen adaptations 221B is the number of the flat and not of the house it's in.

I used to work at Abbey National, which had its headquarters at 219-229 Baker St, and we used to get letters from all over the world for Sherlock Holmes, including one which said something like I know you're not real, but if you were I would marry you. People are quite odd things