Thinking about a conversation I had last week, I wonder how many times I have been asked whether I have some appropriate qualification relevant to the subject matter of the archives I catalogue. To which I think any archivist would respond that there are basic principles of archival practice and it doesn't really matter what you deploy them upon, providing it's an archive of some sort. Actually, I think this has mostly arisen in the context of am I a proper medical doctor (no, my PhD is in fact in history of medicine, so perhaps I am licensed to apply leeches when needful...). I don't think anyone assumed, when I was at the India Office Records, that everybody there was an Old India Hand or had even visited it in the days when it was at the end of the Hippy Trail. (It does help to have some knowledge rather than a completely blank slate to work with.)
That having been clarified, people may want to know if there are rules for cataloguing a particular archive, to which the response is usually, it depends. Just because a particular arrangement was appropriate for one archive, doesn't mean that it can be generalisable to all archives, because every archive is unique, and probably idiosyncratic, outside of certain bureaucracies which stick to protocols laid down in the heyday of public administration. Individual repositories may have local conventions, and certain kinds of records may fall into recognisable structures. But particularly when dealing with personal papers, anything goes, or can go.