Voynich words evolve over a linear sequence

[Jorge_Stolfi]

I think your example with books is surely valid, but too simplified for the work @npcompl33t is doing.  Having only the heights (one dimension) I agree with you that's impossibile to determine if the varying heights are due to a temporal evolution, but when the dimensions are many (the colour of the covers, the paper quality, the font size etc. etc.) and they co-vary this is a strong indication that there's an underlying evolution.

But, again, there are dozens of attributes of a book that are significantly correlated to its height -- like width, thickness, volume, weight, margin width, letters per page, total text length, number of paragraphs, number of the last page, length of the index, thickness of the cover, ...  And yet the ordering of books by any of these attributes, or any combination of them, will still have no relation to time.

Example: we have books 10 cm high with a blue cover and books 10 cm high but a red cover, then 9 cm high an blue, 9 cm high and green, 8 cm and green and so on. I think it's quite reasonable to conclude that the evolution probably was (10cm, red) -> (10cm, blue) -> (9cm, blue) -> (9cm, green) -> (8cm, green) and so on.

That is not a reasonable conclusion at all.  Publishers do not choose the size of a book or the color of its cover in some strict ordered sequence.  

If indeed you see a correlation between the size of books from some publisher and the color of their covers, it may be simply that many of those books are parts of series with similar size and consistent styles.  Langenscheidt published many "pocket" dictionaries with the same small size and a characteristic bright yellow cover. Springer issued thousands of Lecture Notes in Computer Science with red and silver cover, and many Lecture Notes in Artificial Intelligence with blue and silver covers.  But all those books were published over half a century or more, interspersed with other books with other sizes and colors.  

As you know, I also don't agree with you on the statement that 'the statistics of a text mainly depend on the topic, author, style etc. etc.'. ... Italian texts hundreds of years apart, with different topics and literary genre all clustered together for instance on the bigrams statistics.

Sorry, I was considering texts in the same language.  Which is almost certainly the case of the various sections of the VMS -- including "Language A" vs "Language B."  

if the language is the same, then the topic, style, and author are more significant factors for text statistics than the mere passage of time.  Therefore, the statistical similarity between (say) Bio and Stars cannot be taken as evidence that they were written closer in time to each other than to (say) Herbal-A.  It may well be due to both being about similar topics, and thus using similar words, sentences, verb tenses, etc.  The temporal sequence may well have been Bio-HerbA-Stars or any of the other 6 possible orders. 

the quite borderline List of daily Saints of the Catholic church

But the style of some sections of the VMS could be just as "borderline".  Like the Alchemists Herbal in the original Latin:

• Si esset aliquis qui haberet membrum fractum videlicet ossum. Accipiat de ista herba et pistet cum asongia castroni et empastrentur et ponatur emplastrum super feritam aut fracturam ossis et saldabitur os vel vulnus. Item si femina non posset concipere filios, comedat de foliis istius herbe per spatium XL dierum; subitio concipiet utendo marito suo. Item si quis habet linguam paganam. Accipiat folia istius herbe et confricet linguam superius et inferius et subito curatur. Item si quis habet dolorem propter aliquam decensionem de alto. Accipe de ista herba et fac pulverem et da ei bibere cum bono vino per spatium XV dierum et liberabitur a dolore. Item si quis esset crepatus; utatur de ista herba et subito sanatur.
  

Note the repetion of words like item and accipiat and herba/e/is and the excessive use of et.  And the repetitive structure 

• Item si [someone][condition]. Accipiat ista herba et [procedure] et [resolution]
  

with a certain repertorie of variations.  These style features will skew the word frequencies, which in turn will skew the character and bigram frequencies.  And another section may have a style that is just as peculiar, but in a very different way -- which will bias the statistics in a different direction.

And comparing bigram statistics makes sense only if the spelling is mostly the same.  If you take a text in German with umlauts and the standard spelling, and another text  with ue/ae/oe and where "sch" is written "x" and "ie" is "i" and "ch" is "q" or "shh" depending on being hard or soft, you may well conclude that they are more different among themselves than either is to Basque or Armenian or whatever.

All the best, --stolfi