Household ID for decennial census data 1900-1940 (not IPUMS) does not seem unique


I’m using census data for 1900, 1910, 1920, 1930, and 1940. The data is not from IPUMS, but I was wondering if anyone had any advice for a problem I ran into. The household id variable does not seem to be unique; multiple households are coded with the same numeric value. Does anyone have an idea why this might be, or how to get around this issue?

Thanks in advance!