The CLI member organizations numbered the search requests they received consecutively. The CLI staff added a letter in front of these numbers. This letter indicated which organization had submitted the respective search request to the CLI. A separate letter was provided for each member organization. If the CLI received another search request for the same person, no new index card was created. The index number of the second case was noted (usually by hand) below that of the first case.

In this example, the index number D 24521 refers to a search request that was received by the Hebrew Sheltering and Immigrant Aid Society (HIAS) and registered there under the number 24521.