A piece of feedback, I think the paragraph containing this should be moved forward to the part where roll mechanics are explained, as I had to read through that and the techniques before found what the paragraphed TNs mean.

Seconded. I'm reading the book in order and am reading techniques now. I had no idea where to find this information because it's introduced before it's explained in the text (I had to come here to confirm what it meant.) Since it shows up so much in resisting effects, it might be good to introduce it or add a reminder about what the parentheses mean under the explanation for resisting.

Or, something else that would make it clearer on first glance is to add "TN" e.g. "TN 3 (Earth TN 1, fire TN 6)"

That's a tiny fix that would go a long way towards helping clarity a LOT.