Why do the schedules used in the 1790-1820 censuses differ?
From 1790 to 1820, the U.S. Marshals conducting the census only received instructions about what to ask. Each marshal supplied his own paper and used whatever method he chose to divide the paper into the columns needed to collect the required information. The method for recording the data was not standardized until 1830 when marshals received uniform printed schedules.
The columns, rows, and headings on early census schedules, like this one from 1810, were printed by hand.
No two schedules were exactly alike.