For those unaware, the Voynich manuscript is a mysterious book carbon-dated to the 14th century written in a script which has yet to be deciphered to even the slightest degree. It's a really amazing artifact and I encourage anyone unfamiliar to look it up.
There are two main theories explaining the document. One is that it's a forgery with no meaningful content hidden beneath the surface - something made by a wily alchemist to impress a buyer with lots of money.
But the theory I find more interesting is that it's the product of some strange convergence of languages or cultures for which we have no other evidence. For example, it's Mandarin as transcribed by a European using a writing system created 'in the field'; it's an incredibly obscure form of medieval Italian mixed with travelling Romani; it's nothing but very dense Latin shorthand, etc.
Rather than asking which of these is true, I want to ask historians of medieval Europe (surrounding the 14th century) how likely it is for there to be linguistic cultures or ethnic groups from this era that we either no nothing about or which only left comparably slight evidence.
You are asking to answer a question based on a faulty premise. You don’t want us to speak to the authenticity of the work, but rather to hypothesize on possible people who may or may not have existed who’s existence could not be used to demonstrate the authenticity of this document regardless.
The cold hard truth is that historians of science and of the early modern in general see this as a novelty at best and most likely an outright hoax.
You claim that it is from the 14th century, but this is untrue. The vellum is dated to the early 15th century, which means that it could merely be a palimpsest, which is re-used vellum that has been written on after the original writing was erased. Given the value of vellum, this was a very common practice.
Even if there is an early provenance for this work, which is doubtful, Occam’s razor still points to hoax, being as people in Northern Italy were busy trying to sell any book that they could claim was 1. Old and 2. Neoplatonic. There was a fairly robust trade for books taken from tombs, for instance.
Many of these works were faked, and this faking of works only increased during the early modern. It does not help that the Voynovich manuscript’s provenance cannot be traced beyond the 19th c, that the only direct attachment to earlier dates outside the age of the vellum is a letter dated from the 1650s—a period of general resurgence in hoaxes (even Charles Boyle was taken in by these)—and the earliest name given as an association to the work is Edward Kelley, an absolute charlatan who’s professional career was entirely centered on duping the far more respected John Dee into giving him money and letting him sleep with Dee’s wife because Angels told him so.
So, to recap, you are asking a question of historians in which you expect us to forego the entirety of the very very dubious historical record concerning this item in order to postulate on the existence of a non-historical people.
Sources: *Frances Yates, Giordano Bruno and the Hermetic Tradition *—Theater of the World *IRF Calder, John Dee Studied as an English Neoplatonist *M Causabon, A True and Faithful Relation of What Passed for many Yeers Between Dr. John Dee ... (1659) *Deborah Harkness, the Jewel House: Elizabethan London and the Scientific Revolution *K Lesley Knieriem, Book-Fools of the Renaissance, found here: