The Modern Forgery Hypothesis

[asteckley]

The Barschius letter is a genuine letter from the 17th century, from a man known to be a close frend of Marci, and who left his library to Marci in his testament. 

All this is historical fact, from documents that Voynich had nothing to do with.

It doesn't seem that anyone has questioned any of that.

The letter describes a book written in unknown characters, with a great many pictures of herbs, stars and things looking like chemical symbolism. The herbs are described as unrecognisable. Let's call this book 'A'. 
It really existed and Barschius owned it.

Presumably true -- there's been no reason to doubt the authenticity of the letter or that its contents are honest.

 
The argument is now, that book 'B' is a modern fake created by Voynich.

That is one reason that the description is of concern. It is also important because the entire theory of the provenance of the VMS hinges on that description. 

And, while it may be hard for some to understand, whether the scenario around the genuine manuscript theory is certain or not is relevant to discussions of any theory about the book being fake.

 
Can it be a coincidence, that Voynich created a book written in illegible characters, with mostly pictures of herbs but also stars and other things (yes, nymphs), supposedly from Prague, that so closely matched one that actually existed (our book 'A').

We are not talking about another 'complete works of Cicero' here. This is a very specific and highly unusual book.

Absolutely yes -- it could be a coincidence. There are many books of herbs from that era. There may be books also including stars.   And almost all of them include "other things", but, in particular, things relating to alchemisty. It would not be at all surprising for another book to match that description equally well.

That we haven't found one does not prove it does not exist.
In fact, both of the golden arguments that are so often used against any possibility of a fake VMS apply:
  - Absence of evidence is not evidence of absence.
  - 95% of all historical documents remain undiscovered.

 
So no, also Rich understands that this cannot be a coincidence, and it is therefore proposed that Voynich must have seen the Barschius letter, and created the fake (book 'B') based on it.

I avoid speaking for what Rich thinks or for anyone else, but in this case I think I can say no -- Rich understands your argument well enough, but also recognizes it is not fact (which with all due respect, you seem not to.) That the letter is actually describing the VMS is a a definite possibility -- but it remains a supposition. 

And it's important to note that supposition is largely made based on the connection of the VMS back to Marci due to his letter being found colocated with the VMS 250 years later in 1912. And that discovery by Wilfred, itself has suspicious circumstances.   (Because let's face it.. if Wilfred acquired the book and that letter was in the front-piece, it is huge stretch to believe he would not have immediately seen it and been compelled by the date and signature to immediately translate it. ) 

 
Now, the argument is, that Book 'B' must be a fake, because it supposedly does not sufficiently match the description in the Barschius letter.

No -- that is not the argument. Rich is not arguing that the insufficiency of the description causes B it to be fake. The fact that the description could easily be referring
to a different book is important because it directly impacts the generally accepted provenance of the VMS (book B).  In fact, the ENTIRE evidence for the provenance of the VMS between ~1438 and 1912 hinges on that letter describing the book B and no other book.

Think about it.....

The book 'B', created based on the description in the letter, does not really look like the description, and therefore it is the book based on the description in the letter.

The description is not inadequate because it does not describe the VMS (as a potential forger might leverage); it is inadequate because it does not describe the VMS well enough to single it out from all others (which is what the entire provenance of the VMS depends on.)

I have argued this before, and perhaps I was not explicit enough. This time, I think that I was, and I will leave it at that. 
Everybody may form their own opinion about this. I may not hold it against you 

You have been fairly explicit. But you have not recognized the actual claims being made nor why your argument misses them. (And I don't hold it against you.)