The sorting of the CLI followed an alphabetical-phonetic system (Soundex), according to which the surnames of the persons searched for were coded. The initial letter was retained. While the consonants were assigned numerical values, vowels (a, e, i, o, u) were coded as "silent". The initial letter and a three-digit number sequence formed the code.

With the help of this coding, names with the same pronunciation could be sorted together and matched despite different spellings.