Different orthographic traditions in Colonial Valley Zapotec

I've been using our FLEx database recently to correlate an intuition I have had after looking at lots of Colonial Valley Zapotec texts -- that there are some patterns in the spelling that are indicative of at least two different orthographic traditions.

I've labeled the two traditions the Mexicanist and the Oaxacanist traditions.  Important texts in the Mexicanist tradition include Feria's (1567) Doctrina and Cordova's (1578) Vocabulario and Arte.  The oldest texts in Zapotec are in the Mexicanist orthography.

Important texts in the Oaxacanist tradition include Aguero's (1666) Miscelanea Espiritual and Levanto's (1736/1776) Cathecismo


I've found two main diagnostics so far:
  vs

1. The Mexicanist orthography imitates the spelling of Nahuatl and avoids use of the letters , even though Colonial Valley Zapotec almost certainly had phonemes /b, d, g, r, u/.   One very frequent morpheme in CVZ is the aspect marker /r(i) ~ r-u-/.  (The two allomorphs are correlated with different verb classes, and the verb classes are correlated with transitivity.)   Texts in the Mexicanist tradition spell this aspect prefix as or .
2. The Oaxacanist orthography has begun to depart from the Mexicanist orthography in the spelling of /r/, and regularly uses and .

doubled vowels

1. Modern Valley Zapotec vowels have distinctions of stress, phonation type, and tone. (Interrelated in somewhat intricate ways.)  Colonial Valley Zapotec must have had at least stress and tone distinctions, though they are not marked in a very regular way in the orthography.  The Mexicanist orthography occasionally marks vowels with a grave or acute accent, and occasionally doubles a vowel.   However use of doubled vowels is relative unusual.  
2. The Oaxacanist orthography uses doubled vowels much more liberally than the Mexicanist orthography.  (At approximately twice the rate.)

The following chart shows the rates of as a portion of all in the four documents surveyed.