This looks great! the spec steps are much clearer now, and the new description is something I wish had been in 402 when I started reading it.

A couple of ideas that I'm not sure are good or not:

1. I realized while reviewing this that the word "placeholder" isn't actually used that often in 402 -- twice in the NumberFormat spec and nowhere else -- and thought it might be worthwhile to provide a definition. I searched around a little for a link to a definition (thinking I'd find it in documentation for CLDR or ICU) but without much success. Would it actually be useful to define the term, either in the text or a link to a relevant definition, or can we assume that anyone who's reading it is either already familiar or can easily figure it out from context?
2. The description refers to placeholders as placeholders in the first clause, and then later as substrings, i.e. brace-wrapped placeholders become represented as unwrapped substrings. To my eye the switch between one word and the other carries an implication that the placeholder and the substring that's yielded when you remove the braces are different things. Starting the description with something like "It represents each brace-wrapped substring ("placeholder") in pattern" could be a way to both clarify the sentence and also define the term.