Cipher or unknown language - historical perspective

[Stefan Wirtz_2]

[..]
Nowadays, we can be certain beyond reasonable doubt, that the Voynich MS is not an example of some old writing system. No other examples have ever been found,[..]

Is there any valid proof for this/your idea here?

There were several languages even in Europe who did not develop any own alphabet until even later than the VMS.
Or who used neighboring writing systems, even changing them during the times.
Or adopted a one-man-solution as „own“ alphabet and shifted later to another alphabet.

What does that mean: „no other examples have ever been found“?
Those more peripheral languages/writing systems did not „mass-produce“, especially not before book printing era. Many minor languages did not start a regular writing culture before 16th oder even 19th century, but this does not exclude earlier stand-alone attempts.
LFD claimed that „95% of old manuscripts were lost“ so I would even expect that only 1 piece of work from a „low-producing“ writing culture was saved until today.

So, how is there „no doubt“?
Just not able to find it out is no proof.