One must make a distinction between Richard Knötel and Herbert Knötel, the last one was quite cavalier to his sources and is one of the reasons of entrenched errors in the science of uniforms, like Tirailleurs du Po - to name one.
It is a pity that those errors run like a red line through the last decades and other works of authors who put these things right are utterly ignored, like Guy Dempsey jr. whose research is usually top notch.