I had a look at the Probate Calendar entry - should have done that earlier! - and noticed that Alexander is "domiciled in England". The fact that this is specifically referred to in the Probate entry suggests to me that there must have been some reason to doubt his legal domicile, for instance because he had chosen to live overseas for some period.

An address being missing in one census year is a misfortune, but in two consecutive years looks like carelessness (to paraphrase Oscar Wilde). Have you used the street indices at http://yourarchives.nationalarchives.gov.uk/index.php?title=... to look for it?

Hope this helps

Caroline