IMO
organization is a function of the size of the collection, and
how the people using it access the material (and how their minds
perceive the structure of the material).
For small collections (everyone will have their own idea what the
numbers are for them). Random access usually is sufficient. (i.e
a shelf which one "flips" through to find the desired item.
For "medium" collections - some structure is necessary to efficiently
retrieve the desired item - this could be by genre, artist, composer,
etc. Access is by going to the appropriate "section" of the collection (e.g. Blues, Folk, Jazz, Shows, ..... and retrieving
the desired item by sub-sort on title, composer, performer.....)
I've read that there are some people who have organized their recordings by color of the cover - that is what they remember.
For "large" collections a catalog is usually needed to locate an item.
The catalog will point to a location where the item can be retrieved
(Shelving could be by Company label-catalog number, accession number (where items are shelved in order of acquisition, genre-artist/composer/title etc as for medium collections, or other structures meaningful to the user.
If users think of material in terms such as Child Ballad No. xxx,
then a catalog is mandatory. (if the collection has been transferred
to digital media, then it would be possible to arrange items
on an individula track basis - most folks do not do that).
Catagories or genres can be very broad or very narrow. For traditional music it could be localised to a particular region of
a particular country. Categories such as "work songs" "chanties"
etc could be used - whatever is chosen should coincide with the
categories the USER perceives. If FOLK in the users mind covers
everything from Kingston Trio to Texas Gladden, Anglo, and world, no divisions would be useful. If the user perceives differences between "pop" folk, "revival," and "traditional," different cultures
and eras - then more categories ARE needed.
Same sort of analysis applies for other genres, such a Jazz - does the
user perceive meaningful differences between styles, origins, era - then sub-genres become useful (New Orleans, Chicago, NY, Stride, ragtime, Afro-Cuban, et.al.)
Best wishes, Thomas.