That book seemed self-explanatory to me, but maybe it was harder for a non-native English speaker to read and understand.

The main thing to work on is making a BIG difference between the loudness of notes that have accents, and the notes that do NOT have accents.

For me yes it's not my first language but when i read on Dom Famularo book that he said talking about Pull Outs & Control Strokes : "Use the George L. Stone book Accents & Rebounds for further study , Stone actually wrote that book for this purpose but did not explain Upstroke and Downstroke in the text" , maybe even english native drummer practiced that book not properlly   .