In an authority record, 008/14 = 'a' says it's appropriate for use as a main or added entry (1xx, 7xx), 008/15 = 'a' says it's appropriate for use as a subject entry, and 008/16 = 'a' says it's appropriate for use as a series entry (800-830, 440 since we still support it).

In a world where we support multiple subject thesauri, we need a way to tell the difference between a name entry which intends to be used as a main entry and one which intends to only be used as a subject authority, and the way the subject-only one should say that is by having 008/14 = 'b'