Cheryl Lynn Helm discovered decoration pattern in 15th century French manuscript, BnF Français 1745 ( visit here ) that matches one found all over the Voynich manuscript.
Quick search gave me couple more examples. The first one is from BnF Français 5361 dated 15th-16th century ( visit here ).
The second is from Aix-en-Provence library MS 0015, late 13th, early 14th century ( visit here ) where we see the pattern decorating the corners of the picture 'frame'.
Cheryl Lynn Helm found example from c1240, Oxford, The British Library Add MS 49999 ( visit here ).
1486-1506 Book of Hours of Joanna I of Castile, the British Library, Add MS 18852 ( visit here )
1284-1316 The Alphonso Psalter, British Library, Add MS 24686 ( visit here )
Cheryl found two more. The British Library Royal 20 A II, c 1307-c 1327 ( visit here ).
Wiki image of Einhard the Scribe ( we need the manuscript id for this one ).
c 1395-1400 , N. Netherlands, the British Library, Kings MS 5 ( visit here )
1332-1350 the British Library, Royal MS 16 G VI ( visit here )
1420, Netherlands, Bodleian MS Douce D 19
1410, Reims Bibl. Mun. MS 0829
1416, Paris, Reims, Bibl. Mun. MS 0093
1328, Reims, Bibl. Mun. MS 0807
Steve D added the example from Christine de Pizan, City of the Ladies manuscript.
Cheryl Lynn Helm found example from Spain (Aragon) - Paul Getty Museum, MS Ludwig XIV 6 from around 1290-1310 visit here.
Finally, I found one from Germany - Den Haag has it is Western Germany with question mark(?) , 13th century, The Hague, KB, 135 L 20 ( visit here ).
Jan Yperman, Cyrurgie manuscript,15th century
If anybody stumbles on more examples from Germany and Central Europe or anywhere else, please give us ideas!
It would be interesting to get opinion from experts about the history of this decoration pattern.