Why the month names aren't Voynichese?

[Jorge_Stolfi]

Not the paleographer I asked (Baptiste Etienne), who said 15th c. He's right.

I stand corrected, thanks.

But now I wonder how handwriting and book bindings can be dated with such precision.  Did they really change all over Europe, in step, over a few decades?  Were there periodic EU Directives determining the use of new ISO Standards for those things?

All the best, --stolfi