In corresponding with over 200 arthropod collections in North America as part of SCAN I am amazed at the variety of organizational workflows (or lack thereof) among the institutions. Generally, the institution does not seem to administer collections beyond asking how much funding they bring to the institution or how much they cost. Most US collections are based at universities and each collection is typically controlled by the curator. This is generally good, the institution relies on a tenure-track faculty to be successful. But it generally results in fragmentation. Collections typically have more loyalty to the CMS they use than sharing a common institution.
Institutions are generally permanent but the practices of individual collections are very idiosyncratic, changing with each succession in curators. Collections are much more likely to come and go. Most collections probably do not know what their institution code on GrSciColl is and several make up their own when the digitize.
Additionally, entomology collections in the US want to divide collections within a larger collection by taxa. For larger collections, especially at museums they already administer holdings by order or class.
I conclude that defining and tracking a collection is challenging because they vary so much among institutions, and they are not static, they will evolve, divide and combine with time as curators or institutional politics change.