Are Foldouts Always Shorter to Left but Longer to Right?

[VViews]

It is the first time I heard that gathering marks were written before the binding.

Does it mean that the one who wrote gathering marks (9n9 aka nonus) and the one who wrote page numbers (67, 68) might be different persons?

Hi ChenZheChina,
The purpose of the gathering marks (quire numbers) was to group the quires together, serving as an indication for their arrangement during binding.  Quire numbers are typically placed on the final verso of the quire, not just in the Voynich, but in medieval manuscripts in general.
The quire numbers were added before the binding process: afterwards, they are no longer useful.
As for the page numbers, I agree with JKP that they were done by a different person and at a later date.
Page numbers serve a different purpose: they are there more for the reader than for the binder.