AACR2 headings affected by rule changes

Correct the heading and evaluate references accordingly.

If the previous AACR2-coded heading is a valid AACR2 reference to the new heading, retain it and code it ‡wnne. This special coding of the subfield w; is used in all cases when an AACR2 heading is changed (including provisional and preliminary headings) and the previous AACR2 heading is now an acceptable AACR2 reference.

If the previous AACR2-coded heading is not a valid AACR2 reference to the new heading (as when the new heading has dates which were not present in the old heading), do not retain the previous AACR2 heading as a reference in the record.
Delete it.

151 0 Sibley (Devon, England)
451 0 Sibley-on-Eyne (England)
451 0 ‡wnne‡aSibley (Devon)