The ISAD(G) standard, around which AtoM's templates were first designed, unfortunately does not include a definition for "accumulator," but it does have a definition for creator:
Creator. The corporate body, family or person that created, accumulated and/or maintained records in the conduct of personal or corporate activity. Not be confused with collector.
Note that this can be different from the author. For example, in an office, one particular member of a committee may be responsible for authoring a meeting minutes document, but the "creator" would most likely be the committee holding the meeting and not the individual who happened to type them - the act of writing does not necessarily always correlate with responsibility for creation.
- The organic process by which a collection of records grows out of a routine process.
- Preservation and Conservation - A deposit of foreign matter; an accretion.
Accumulation(2) connotes a substance that increased over time, although it may no longer be growing.
I hope this might at least contribute to the discussion!