The Voynich Ninja

Is it possible that the reason that the Voynich script appears to have only 13 or so letters (when accounting for positional variation) is that multiple letters could use the same glyphs? This phenomenon can be found in early Arabic writing. In the Arabic script, there are many sets of letters which are only distinguished by the i'jam, small dots written above or below the letters. However, in early examples of the Arabic script, such as the Burmingham folios, only the rasm is present, and not the i'jam (or harakat). This leads to many sets of letters appearing identical in some or all positions, despite them making completely different sounds. This causes the script to appear to only have 15 distinct letters, despite actually the Arabic script actually having 28 letters.

Is it possible that the Voynich manuscript exhibits a similar phenomenon of multiple letters appearing identical in some or all positions, and thus actually has a larger alphabet than it appears to?