The inner bark of young shoots is the medicine for willow. I am just now watching a video on how to collect willow. Warning, the camera work is quite bad.
While his method is valid, he actually does it the hard way using older branches and scraping the inner bark. This would be the “purists” way.
Patrick and I like to use the very young branch tips and just use the whole of the material. You can dry and grind it or you can make a tincture with it. Yes, there is some of the material that might not be medicinal, but who knows! You at least know you are getting ALL of the medicine out of the branch and not missing any in the scraping process.