I wouldn't worry too much about what his keywords are, some mean what they are supposed to mean but most are either in-accurate or completely off the mark.
The general idea of the keywords is just so you have a handle to remember and recognise kanji until you can replace them with proper meaning and readings etc. so at the end of the day it doesn't really matter that much.
You'll start seeing the more used and common kanji later on in the book, why it was done in this order i don't know but if you complete the whole book then it doesn't really matter.
RTK is only useless if you try to use it for something that it's not supposed to do.
For example it's not supposed to teach meaning, just how to write and how to remember, if you use it for this and only this then it's a great way to learn stroke order etc. of all the kanji in a
stupidly short amount of time.
So anyway, the point in my post is just to check that you aren't trying to learn his keywords as the actual meaning of the kanji, since most of them aren't anywhere close to the proper meanings anyway, and to let you know that a lot of the first part of the book contains a lot of kanji that aren't used very often or not at all from what i've seen.
Sorry if i mis-understood, it's just that a lot of people who try RTK go into it not reading the introduction and thinking that his keywords are the actual meaning of the kanji, and thinking that all of these kanji are used in every day life, which as you have seen from 吾 that they aren't
