Not ignorance at all! I just have an advantage because I'm older than dirt.
The cloth ribbed material represents the canvas that carried the cut grain upward to the threshing cylinder which separates the grain from the straw. This was the case on the 12-A and the 25 combine that replaced the 12-A.
The yellow rotating bars do indeed bend the wheat/oats/soybeans/clover seed, and, in one case some 55 years ago, a small patch of popcorn, down to enable cutting the grain. This is called the reel.
The "30" combine had an auger which moved the cut grain to the center of the platform and then into the threshing cylinder.
I'll send you a couple of pictures by separate e-mail which will clearly show the difference. Please send me an e-mail at firstname.lastname@example.org so I can send you those pictures.