I think these are the key insights behind Picture Notation. Adding the syllable system for candidate pieces eliminates the remaining uncertainty. Interesting to hear you use flashcards too.
If anyone is interested in book progress: I have jumped ahead to chapter 7, which attempts to answer the question a few people have raised, Why should you memorise theory (using picture notation)?
This is quite a long essay, which reaches the conclusion I wrote in the comments above: picture notation doesn’t replace chess understanding, but it does let you play your theory perfectly. This in turn reminds you of your plans.
I also explain spaced repetition and some side topics. I find mnemonic techniques for blindfold simuls very interesting, so I discuss that too.