Issues with 1851 Canada Census
1. Some records indexed as 1851 are actually 1842 Census. Going back through microfilm images to beginning page confirm as 1842, and format matches 1842 census found on Canadian Gov site (primarily only 1st page had column headers and only head of household listed by name.) Example: https://familysearch.org/ark:/61903/1:1:ZPSS-16PZ
2. It appears the 1851 census was indexed twice but only 1 version includes an image. There are errors in residence that appear on 1 version but not the other making it look like similar families in 2 different places, but only one can be cross-compared with the image. Example: the Perth, Lanark, Canada West records have been incorrectly tagged as Pakenham, Lanark in 1 version and some also mixed up with Drummond, Lanark in the other version. This is confirmed by checking the village/township name on the backside page of record or scrolling back through images to find start of township.
3. In this time frame, many people born prior to 1841 are listed with "Upper Canada" as birthplace. However, often the abbreviation "U.C." was used and the search results are interpreting it as Australia. Once you click into record and see indexed info there is no reference to Australia, just the initials.
4. There's also many instances where records from UK census are coming up in Canadian search results where the UK residence is reverting to a Canadian one of same name, when only village/township is listed. Possibly due to incorrect standardized location. Example: Henly in Somerset, UK comes up as Henly in Niagara, Ontario. So people appear to incorrectly have a Canadian residence on a UK census.