Why the month names aren't Voynichese?

[ReneZ]

The sign of Gemini, for instance, today approximately goes from May 22 to June 21, but by 1430 it was approximately from May 12 to June 11.  Thus the label "June" on the Gemini sign has been "1/3 wrong" since 1582 but would have been "2/3 wrong" when the VMS is believed to have been written.  

There was a discussion about this here, probably just before you joined, where the case: 'month in which the Sun leaves the sign', matches the assignments in the MS, and this was also used in some historical examples.
Apologies for my inexact recollection.

Also Toresella said that the month names are in a 15th century hand, but indeed this could be several decades later. [Edit: later than the creation of the MS]. Plenty of time for the MS to have travelled to France. (It is not certain that it was there).