I discovered that there was an amazing amount of people missing from the 1901 census in England. Having done an interim census, I think you have to put some of it down to the human nature of the emunerator at the time. Maybe there was not the incentive to go back to the household; or maybe incomplete households were logged. Who would know in the case of shared properties? A lot of reasons for not wanting to put too many names on a form! My guess, anyway.