The Voynich Ninja

There are several small letters written in the upper corners of several pages in the "cosmological" section.  I've collected all the ones that I could find and put them along side the first three letters of the "erased key" on You are not allowed to view links. Register or Login to view. for comparison:



Several questions:

• What purpose did these letters serve?  Did it have to do with an attempt to put these pages in the correct order?
  
• Are there two different hands in this marginalia?  The letters on f68 appear quite similar to the erased key, but different from both the "a" and the "b" on f67 and f70.
  
• When and where were these letters added?  Is there anything paleographically distinctive about these letters that might point to a particular time and place?  More specifically, is it likely that these letters were added during the Prague period, or were they added before or after that time?