Why does the number before the hyphen change between the 1930 and 1940 censuses for some locations?
In 1930, the Census Bureau decided to assign two-part numbers to each ED. The first part of the number (prefix) denoted the county within the state, and the second number (suffix) denoted the census district within the county. The ED prefixes were usually assigned sequentially to the counties in alphabetical order, so a county like Adams might be given a prefix of 1. Similarly the ED suffixes were usually assigned in alphabetical order by city name. To make things confusing, Ancestry.com does not show the full 1930 ED number, but just the suffix. In 1940, the Bureau extended the 1930 prefix numbers by assigning unique prefix numbers to the largest cities within the United States. Such city prefix numbers come after the highest county prefix number within each state. For example, the Hollywood Knickerbocker Hotel is in the city of Los Angeles, and that city is within the county of Los Angeles. In 1930, Los Angeles county was assigned prefix 19, and the Knickerbocker Hotel was assigned E
