The info in the NSCA journal is correct. The “constant knee angle” is meant to explain to the reader that you don’t squat the weight down or lock our the knees as you finish the lift. Also, for the purpose of teaching the hang clean, it is important to break the lift down into seperate parts, thats why the stance is slightly wider than shoulder width, to prepare the lifter to incorporate the technique towards the hang clean. Most coaches teach the lift with a stance inside of the shoulders. The RDL is not a stiff leg deadlift, the movement is all in the hips, pushing the butt back, ect. The back must be kept in neutral the whole time, and the knees must be slightly bent at all time. The bar stays close to the body throughout the lift. You are esentially taking the hips away from the bar and then bringing them back towards the bar. The RDL is much safer for the lower back than the SLDL.