There are a few problems inherent in the SuDoc system.

One of the most important is that over time offices may be reorganized and come under the authority of a different agency. In that case, the call number changes even though the publications are from the same agency and are about the same type of information.

The Classification Manual published by the Government Printing Office gives the example of the Institutions of Higher Education Index. It had the call number HE 19.322: indicating the parent agency to be the Department of Health, Education, and Welfare.

The office that published the index was moved to the Department of Education, so the call number became ED1.116/2. Someone needing publications before 1980, when the change occurred would have to look under the HE. If they wanted information published after 1980, they would have to use the ED call number.

The correct call number for the date requested is in the index you used to get the call number originally, but if you want to browse, and find nothing, remember this quirk and if you have a question, ask the Government Documents Librarian, staff or student assistants, or any Reference Librarian.