RDA defines Other title information as a word, character, or group of words or characters that appears in conjunction with, and is subordinate to, the title proper of a manifestation (e.g., subtitle).
Is required only if it provides clarification or support to the Title proper that otherwise might appear misleading without the Other title information (CONSER) or when the statement of responsibility is embedded in the Other title information (RDA).
Record Other title information only from the same source as the Title proper (RDA 2.3.4.3). Statements that would normally constitute Other title Information that are found only on other sources may be given in a note.
Subtitles
The most common type of Other title information is the subtitle. In order to decrease the need for maintenance given the frequency by which subtitles change, CONSER practice is to transcribe the subtitle judiciously and when it provides clarification to the title proper.
245 00 $a Computers and libraries : $b an Australian directory.
245 00 $a Montana: $b the magazine of Western history.