Thanks for the additional info. Now for the rest of the story. The Midori is (as one put it) a flap of leather with some elastic. The scheme for putting 3 notebooks in that flap of leather is a little bit clumsy (in my view). I've found an alternative method for threading the elastic cord so that 3 notebooks can be added, removed or changed more easily.
Today, I picked up some 4-5 oz veg tan. Over the weekend I expect to make a couple of prototypes. Cutting the leather to size and shape and punching holes will be easy. It's the finishing where I'm inexperienced. The Midori in the video is certainly darker than (raw) veg tan. However, I couldn't tell whether the darker color resulted from dye or the old baseball glove treatment with neatsfoot oil or something else. Or, was it some sort of oil tanned leather?
Each of you has added to my knowledge and, after visiting Tandy, I've got some ideas about how to finish the leather. I'll post some updates when I've got something to show.
Again, many thanks!