Bib isn't updated when new authority-controlled subfields are added to auth record

[viola-v]

Jessica flagged this issue:

All of these records are linked to the same 991 authority: https://metadata.un.org/editor/records/bibs/search?q=xref:938768&subtype=all

The authority was initially created without subfield b, and the bibs were attached when there was no subfield b.

Then subfield b was added, but the bib records weren't updated accordingly.

We will need a report to identify all instances of where this happened (including other authority-controlled fields) after the code has been fixed.

Possibly related to open issues #1262 and #1314 .