Although most are based on the name of the department, X and Y call numbers aren't. X and Y call numbers aren't based on the name of the Department. SuDocs is not a decimal system. SuDocs is not a decimal system.
Years come before numbers.
This is the correct SuDocs call number order. This is in decimal order, but SuDocs is not a decimal system. Years in call numbers are 3 digits until the year 2000. Years from 2000 forward will be four digits. Years from 2000 onward will be written as 4 digits.