[split] Did the VM go straight from cerebellum to vellum?

[oshfdk]

...

I just asked whether you have a source. I'm not sure a discussion about how plausible it was and whether writing directly on vellum was ever reasonable or not makes any sense, if we only base it on our estimates of the realities of the time by using modern analogies. There is certainly nothing physically impossible or "insane" in writing directly on parchment, all your arguments, even if correct, only point towards this as not very efficient way and a recipe for some lost money, which could be or not be an issue, depending on who any why created the manuscript. 

If the author wound't even use a good enough tool for drawing the circles and, according to you, miscalculated the arrangement of various elements on a few occasions, it's less likely that there was a proper draft first and more likely that the whole thing was designed immediately on vellum. And also it's certainly possible to do some drafting or sketching on vellum with a sharp tip instrument.