Why I think that the copyist(s)/scribe(s) did not fully understand the material

[N._N.]

Unlikely indeed.  

I wonder how many here have read Stanislaw Lem's tale of the guy who set out to find a Genius Of The First Kind? (That tale and his novel His Master's Voice should be mandatory reading for admission to this forum.)  

In the relevant time frame there must have been thousands of Geniuses Of The First Kind who invented a new script for some reason and used it to write a VMS-length book.  Societies with half a dozen members who did the same must have been much fewer, in the dozens or so at best.  So multiple Authors is a priori  far less likely than single Author.  Until we have evidence of the former (such as another document in the same script that is clearly by a different author), it is safer to bet on the latter.s

Since we pretty much know that there were multiple scribes, there must be more to it than just a single 'genius', even if we cannot really know what the role of the others were (just scribe without knowledge of the manuscript's meaning/scribe with a basic understanding/scribe and author). Additionally, the purpose of a cipher/language is usually communication, which requires multiple people. With these points in mind, the general theory about the circumstances of the creation of the cipher manuscript must be weighted against the factual evidence about the number of scribes etc. In my opinion, it is impossible to reach a final conclusion about the number of authors.