It is well documented that the same text, indexed by several indexers, will result in as many slightly or even substantially different indexes, and even the same indexer will produce varying indexes for the same text at different times.
The indexing problem changes with each new book undertaken. To meet the needs of different classes of seekers and to suit various types of books, rules entirely satisfactory in one case must be varied in the next and perhaps ignored or even reversed for a third... Indexing is a highly complex intellectual process involving the use of language in a specific and somewhat artificial way, and that it is also to a considerable extent a matter of intuition, the workings of which cannot be reduced to fixed rules. It is 'knowing what but not knowing how'.
We know that we can do it, but cannot describe in so many words how we do it, nor can we reduce it to a set of rules. At most, the observable facts of the indexing operation can be described.
Importance, like beauty, is in the eye of the beholder and that there is nothing inherently "logical" about the preference of users in looking for one component rather than another of a compound heading.
There is no such thing as "the user". Users... come in all shapes, sizes, and colors, and they have widely varying information needs.
Detailed analytical indexing is generally the hallmark of good back-of-the-book indexes.
