I looked up my mother's family this morning. My grandmother and her 6 siblings don't appear to be on the census (confirmed their birthdates with the same website, Findmypast). Also missing my great-grandmother & great-grandfather.
Other alternative, that my mother disagrees with is that they were there but their birth dates have been recorded incorrectly because they were living with relations. I thought this was more likely but then checked the birth records and it does appear they are different people, just with the same names.
How does one go about checking that the indexers haven't missed off a whole street somewhere?