@NiLuJu Just adopted that practice myself for the Kindle Knowledge structure.
Indexing by "first 4" with tags and/or notations of the more common names that have been in use.
Still mostly empty pages there, so a good time to revamp how things are presented to the reader. After I have had a good night's sleep, will implement more of the different scheme.
It will be interesting to see how Amazon numbers things, because with the introduction of the Kpw - it is either part of the "5" series or jumps to "7 or greater" because the Fire is "6".
So I am expecting some numbering problems here with the K2, K3, K4, K5 ... terminology.