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

[Torsten]

But the VMs doesn't even contain visible corrections....

It does have corrections. Many of them. But they are minor, usually limited to parts of individual characters.

My formulation was indeed not precise enough. 

With corrections I mean changes that affected the layout of the text. If the text was copied I would expect that sometimes miscopied glyph groups were scratched out and replaced. But there are no scratched out places.

In the same way it is noteworthy that the last glyphs in a line are never squeezed into the available space. Even holes in the velum didn't mean that the scribe was running out of space.