B4.2.3. Other changes
Subscription date (037) [O]:
If the subscription data is no longer valid, it may be updated or deleted.
Frequency data (310/321 [O], 008/18-19 [R] ):
If current frequency is known to differ from data in fields 310 and 008/18-19, change tag 310 to 321, add a new 310 field, and update fixed field 008/18-19 to reflect the new 310. Add relationship dates, when known, in subfield $b of both fields 310 and 321. Note: fields 310 and 321 are optional in core records.
See also: