I have been using the term "Dysfunction In Possessions" ( DIP ) to refer to the clear physical manifestation of "a mess" in question.
This doesn't include any assumption as to its causes, timeline or outlook, or whatever contributing factors, whether personal or systemic.
This is the one real, observable fact in those situations the "experts" refer to as "hoarding".
DIP will vary in scope and degree - any part or whole of a room / storage area / piece of furniture may be dysfunctional, while others may be completely fine, and the extent of dysfunction in any given area willl vary.
Concerns of health, safety, access to facilities are paramount in importance, and must be addressed ASAP.
Systems Approach should be used to examine any given situation as to its causes and mitigation measures -
* nature and structure of contents
* intentionality / person's intentions ( to perhaps better guide solutions )
* contributing factors
** resource shortage ( time, money, space, attention ) to process / organize / complete projects / clean up / purge ?
** conflict ?
** disability ?
** competency ?
** other factors, without loss of generality ?
* timeline of development
* flows - inflows ( acquisition ), outflows, imbalance, rate
* processes - receiving, organizing, accessing, using / consuming, disposing