secondary defenders, nor mention of feet being set, one way or the other. It sounds to me as if your hangup is in the definition or interpretation of the phrase "legal guarding position," with the former NBA coaches interpreting that phrase to mean that feet should be set at least momentarily, and you interpreting that feet don't need to be set at all in order to establish a "legal guarding position." I don't see anything on page 45 that makes their statement or interpretation incorrect.
Without better evidence, I will continue to trust the interpretation of the former NBA coaches/players/analysts for now. Sorry.