Heck, in the US census records, there are gaps like that. I have searched and searched the 1850 US census for New Orleans, La. and cannot find persons I know to be alive and living in New Orleans at the time. I think, at least in the US, some census takers just did not find everyone. Or, sometimes, the records are so faded or illegible, the software cannot read them. In one case, an ancestor did not turn up on the index because the census record was so faded.