Arrangement notes - smith-special-collections/sc-documentation GitHub Wiki
See DACS 3.2
Describe the current organization of the unit being described. At the collection-level, an arrangement note should explain the series or other structure in the collection, but does not list all of the series in the arrangement note. For example, a note may say that "materials are organized in series by document genre," but need not list all of them, since ArchivesSpace provides that listing as part of the sidebar.
An arrangement note does not entail information about rearrangement of materials or maintenance of original order, which would be described in the Processing Information note.
Arrangement notes are optional. They should be included when it is not immediately obvious what the method of arrangement is, or if there are subseries or other complexities to the arrangement. The arrangement note is primarily for the benefit of the researcher, and should be included if such a note would be likely to assist a researcher looking at materials for the first time.
A collection that has had new accessions added to the end after processing might have a note similar to the following:
Materials in this collection received before 2005 are arranged into series by type of material. Materials received since 2005 have been added to the end of the collection as one new series for each accession.
All collections that contain material arranged by accession should have the following note at the resource level:
This collection has been added to over time in multiple "accessions." An accession is a group of materials received from the same source at approximately the same time.
Generic text for collections that do not appear to have been arranged:
The collection has not been arranged since it was accessioned and is most likely in the order in which it was received from the donor.