Colour images of the Utrecht University Library fragments (mostly c. 1400) can be found by following the link:
http://digbijzcoll.library.uu.nl/lees_gfx.php?lang=en&W=On&BoekID=016012&PageOrder=14.00
Many thanks to Rob Wegman for noting this link in the Facebook Group Ars Nova: Group for the Study of 14th and Early 15th c. Music.
The early 20th-c. article (in Dutch) on this fragment, Muller, J W: 'Brokstukken van Middeleeuwsche meerstemmige liederen' Tijdschrift voor Nederlandsche Taal- en Letterkunde (1906), can be found at:
http://www.archive.org/det ails/tijdschriftvoor06leid goog
Enjoy!
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RISM description available on DIAMM at:
http://www.diamm.ac.uk/jsp/Source.jsp?navToggle=1&sourceKey=754