Related to BB-462 there are many other identifiers we can glean from wikidata: https://www.wikidata.org/wiki/Q1323220

• https://www.wikidata.org/wiki/Property:P950 BNE identifier (iblioteca Nacional de España)
• https://www.wikidata.org/wiki/Property:P268 BnF ID (Bibliothèque nationale de France)
• https://www.wikidata.org/wiki/Property:P227 GND identifier (Deutsche Nationalbibliothek)
• https://www.wikidata.org/wiki/Property:P244 LCCN identifier (US Library of Congress)
• https://www.wikidata.org/wiki/Property:P349 NDL authority id (Nihon no kokuritsu Kokkaitoshokan) (National Diet Library of Japan)
• https://www.wikidata.org/wiki/Property:P691 NKCR AUT ID (National Library of Czech Republic)
• https://www.wikidata.org/wiki/Property:P1006 NTA identifier (Dutch National Thesaurus)
• https://www.wikidata.org/wiki/Property:P906 SE-LIBR ID (Sveriges Kungelige Bibliotek)
• https://www.wikidata.org/wiki/Property:P269 SUDOC identifier (Système universitaire de documentation)
• https://www.wikidata.org/wiki/Property:P1015 BIBSYS (Norsk BibliotekSystem)
• https://www.wikidata.org/wiki/Property:P723 DBNL ID (Digitale Bibliotheek van Nederlands)
• https://www.wikidata.org/wiki/Property:P1417 EBID (Encyclopædia Britannica Online)
• https://www.wikidata.org/wiki/Property:P7704 Europeana
• https://www.wikidata.org/wiki/Property:P646 Freebase ID
• https://www.wikidata.org/wiki/Property:P5587 Libris-URI Swedish National Library
• https://www.wikidata.org/wiki/Property:P6520 Lokalhistoriewiki.no ID
• https://www.wikidata.org/wiki/Property:P3222 NE.se ID (Swedish Nationalencyklopedin Online)
• https://www.wikidata.org/wiki/Property:P1315 NLA Trove ID (National Library of Australia)
• https://www.wikidata.org/wiki/Property:P3154 Project Runeberg ID
• https://www.wikidata.org/wiki/Property:P1938 Project Gutenberg ID
• https://www.wikidata.org/wiki/Property:P4342 SNL ID (Store norske leksikon)
• https://www.wikidata.org/wiki/Property:P7859 WorldCat Identity ID

see also:

• https://www.wikidata.org/wiki/Special:WhatLinksHere/Q29547399
• https://www.wikidata.org/w/index.php?title=Special:WhatLinksHere/Q55650689&hideredirs=1&limit=500
• https://www.wikidata.org/w/index.php?title=Special:WhatLinksHere/Q19833377&limit=500

a cool ability/userscript/etc would be a button or something to "fetch identifiers from wikidata" once a wikidata link is entered - then any identifiers we have in common with WD could be auto-filled in.