I would consider the publishers as part of this community. They are most likely one of the biggest users of collection codes in publications, and in fact there must be a great interest from the collections community to promote an increased usage of collection codes in publications.
At the same time, the publishers are an important source of collection data that is not in GRScicol, such as data of private collections, alternative acronyms of the same collection, such as BM for NHM for NHMUK that also changed through time.
Finally, publishers also provide the provenience of data, such as this collection code has been publihsed in this article in this taxonomic treatment in this material citation, each of it can be cited using a persistent identifier.
What needs to be addressed is that publishers and this group works more closely together to promote the usage of collection codes to serve the best linking of the two sources. The risk of not collaborating is that collections will have a continued deficit on understanding the use of their data.