In 2015, researchers at the University of Cambridge shined a UV light on an ancient Welsh manuscript and discovered "details hidden in the book that had been erased from history, finding doodles, marginalia and an additional verse" (https://www.bbc.com/news/uk-wales-32133243). Among their findings are the two faces shown below on the right.
They speculate that a later owner had erased parts of the manuscript with a pumice stone to "tidy it up." Apparently, it was a commonplace practice to add and subtract material in this way.
That raises questions about the Voynich manuscript. How much of the original survived? Was any of it erased? Might there be pages or folios out there from this manuscript that have been erased and repurposed? Would it be possible to sleuth lost folios out by an analysis of the vellum and marks, wrinkles, inks, and perhaps even erased script?
The hunt for more of the manuscript would be, as with everything about the Voynich, tortuous. However, the Black Book of Carmarthen gives us tangible evidence that manuscripts can hold stunning secrets.