Are the 1430s the most likely date range for the Zodiac drawings?

[Mark Knowles]

There are two different arguments being conflated here:
a) Is the VM a derivate work of the Lauber style?
b) Can the VM illustrative style be used to attempt to date the period which they represent?

I fail to see why attempts are being made to link one to the other.

Well they are linked as the works of Lauber date from 1427 onward. So if the Voynich central Zodiac Illustrations are copied from a work of Lauber this cannot have happened before 1425. Likewise if the Voynich drawings date from before 1425 then they cannot have been copied from a work of Lauber. So b) and a) are interdependent and therefore linked.