It is this type of categorizing and re-categorizing that prompted the original A-Z suggestion.
If you have a Nokia Cell Phone Users Manual, and you put it in a folder with the first name that pops in your head (cell phone, or nokia, perhaps), then you will likely think of the same thing when you are trying to retrieve it.
Specifically, if I had that particular item, I could file it under:
AT&T (wireless carrier)
... and that's about it.)
If my files are A-Z then it will take but a few seconds to locate it. Note that after putting a lot of things in your files, you will get familiar with your file names and will remember having seen "Nokia" a lot.
If, instead, you categorize by Product Literature--Manuals, or Electronics - Phones - Manuals - Nokia, you only multiply the number of places it can be. Every time you re-categorize, you add more confusion.
There is no division of categories that will be completely leakproof for ANY type of information and will also be simple enough to remember.