[split] Line padding, layout, Currier's "groups of letters"...

[Torsten]

We have evidence that the scribe was choosing little groups of letters to fill out the line to the margin.

I haven't seen this evidence and I would like to see it.

The layout of the text corresponds to the folio. This is evidence enough. 

As described by Currier the lines of the VMs work as functional entity: "the line is a functional entity in the manuscript on all those pages where the text is presented linearly" (Currier 1972). Currier observation was confirmed by the statistical work of Elmar Vogt (You are not allowed to view links. Register or Login to view.). At the same time the end of the lines nearly always fit into the available space. This means the layout of the text corresponds to the layout of the folio. This was only possible since the author of the VMs was knowing every hole in the vellum as well as well as the illustrations. But how was the text generated by its author?

Curriers answer to this question is that the layout of the text was made during writing and that the scribe added fill words if necessary (see Currier 1972).

Your answer to this question is: "Rather than considering a virtual right margin in the final manuscript, I would prefer to consider a true margin in a source document, for example a draft" (You are not allowed to view links. Register or Login to view.). 

Your answer implies that the layout of the text was copied. This would mean that the layout fits only so well since the source document had the same size, contained the same illustrations and the same mechanical damages as the VMs or at least markers for them. In addition, any copying error such as a doubled or omitted 'word' would have resulted in longer or shorter lines. With other words, any copy error would have been immediately obvious. But the VMs doesn't even contain visible corrections. It is hard to believe that the VMs was copied without any errors especially since you assume that the copyist did not understand what he was copying (see You are not allowed to view links. Register or Login to view.). But even if we assume that your answer is correct this would mean that the text we see today is a perfect copy of the source text and was this way intended by its author.