A Soloka (are you the Alan Soroka formerly of UBC?) quoted:
>"Qualifier of title information to make it unique."
By "it" do they mean the title itself?
That definition is a slight paraphrase of the definition for the 222 $b, and by extension the 210 $b as well. According to the script for "module.MBIB-2-BIBFRAME-Shared.xqy" on LC's BIBFRAME GitHub site (not sure how to get a shorter URL for that particular page) this BF property gets its due when converting records with the aforementioned subfields through the MARC-to-BF filter.
222 -0 $a Notes d'information et statistiques $b (Banque centrale des Etats de l'Afrique de l'Ouest)