Do Herbal A and Herbal B correspond to differences in imagery?

[Anton]

This would mean that A-images were drawn entirely by a different artist than B-images. It is possible, but then why is the difference only noticeable in this small detail.

I'd rather say, it has been noticed in small detail, not is noticeable. Practice shows that many details of the VMS went unnoticed for I don't know how long. When one begins a systematic analysis, they suddenly get noticed. Likewise, in this case, a systematic analysis of A vs B drawings would be helpful.

Of course, I can think the other way - maybe this kind of stem separation was used as some marker or mnemonic. So the guy, reviewing the folios afterwards, placed the marker where it was absent (but should have been present).

Regarding the painting, I think it's important to take into consideration that painting (or, at least, some of it) was not applied directly after the drawing. To resolve this question, it is important to determine when the red painting was applied. For example, if it all was applied afterwards, it may have been applied exclusively to places marked with the red colour code. The colour code is hidden under the paint, so we cannot tell if it's there under the paint or not. So the abundance of red in A may be the direct consequence of the abundance of colour codes in A. This is also a very simple explanation.