Here's a closer view. Cartridge pleats are not easy to do, as they have to be sewn by hand every few inches and then attached to a backing fabric to hold their shape. I've sewn cartridge pleats on cotton and it was not fun. I cannot imagine attempting this treatment on heavy wool coating!
This line drawing will give you an idea of the work that goes into making cartridge pleats with the rows of hand stitching. I've never seen this method used for a collar, but it's quite effective, isn't it?