B4.3.1. Pre-AACR2 vs. AACR2 rules of entry
The criteria according to which a serial is determined to have changes its title (or main entry/title) differ between AACR2 and earlier cataloging codes. When a change occurs in a serial represented by a pre-AACR2 record, and that change would necessitate a successive entry as cataloged under pre-AACR2 rules, but Not as cataloged under AACR2 rules, update the record to AACR2.
See also:
B4.3. Changes in cataloging codes or RIs or subject analysis or CONSER practice