I wrote a paper (announcement and link below) containing evidence of the date of f68r1 being 18 July 1533, showing the Great Comet of that year. I’m not going to rewrite the paper here; if you want details, read it.
To further call attention to it, I have made a new page with the diagrams. The link is above. (I am having trouble getting them set the way I want them, so expect modifications.)
The first is the folio in question. The second is a diagram of the comet’s path from Apian’s Astronomicum Caesarium 1540. The third is the folio and diagram overlaid, The fourth is a star chart from Starry Night Pro 4.
This date refutes the idea that the vellum of the VMs was used immediately after creation, circa 1420. Other dates found in the Astro section cluster near the late 15th Century (see the earlier entry).