Historical ciphers, when they were introduced and their effect

[Mark Knowles]

Thank you for the explanation and the link, Marco. I have always wanted to read that text 

So it's both about Greek way of writing numbers and so called monastic sign languages:
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Yet I would say that it's not completely useless for Voynich Manuscript. It shows that people in medieval ages were conscious about different numeric systems. In Roman numerals only few letters are used like I, V, X, L, C, D, M. But in other systems (Greek, Hebrew, Slavonic) every letter is used and every letter means some number.

So if letters may mean numbers then numbers may mean letters, right?  And you can code letters with numbers. And Voynich vords are similar to Roman numbers.

Today a lot of ciphers use numbers and such numeric ciphers appeared already in the 1500s. See the great website Cryptiana for such stuff ( You are not allowed to view links. Register or Login to view. )

But in the 1400s there were no numeric ciphers or almost no numeric ciphers. They became a standard when Arabic numbers became a standard. Voynich Manuscript seems out of place here, like someone was coding words with some mutated Roman numerals.

Arabic numerals were used as symbols in 15th century ciphers. I don't think it was the adoption of Arabic numerals more widely that explain the increased use of numbers within ciphers. There was a natural shift over time from elaborate invented symbols in ciphers, e.g. in Paolo Guinigi's cipher ledger, to the more straightforward, simple and logical use of numbers.
It is a interesting question as to whether the style of symbols used in the Voynich manuscript can be used to date it.