I ran across this one the other day - it does not seem to have been announced here so I am forwarding it in case it slipped under the radar:
1 J0/674 Composition musicale de Pierre de la Rue ou Pieter Van Straeten ou encore Pierchon (vers 1452-1518) 1500-1550
You will need to manually scroll down to item 674, or search for "composition" on that page to locate it in the list of items on the left - there does not seem to be a way of creating a permanent link to the individual item within the collection.
Discovered in 2016 by Alain Cessot & Michel Sanvoisin, the fragments have since been unglued/removed from the host volume's binding. There is a small online article (and one which includes the link to the above image) here:
Bonne année à tous!
(edited to modify/correct links)