Dating Spelling Conventions

[Richley Crapo]

I'm working on a Tlaxcalan manuscript written around A.D. 1600. The scribe follows the spelling teuctli, but a later editorial hand (added after some degradation of the paper had occurred) uses the spelling teuhtli. Is anything known about when that spelling (teuhtli) arose or where? I'm wondering whether this spelling difference can be used to say anything about how much later the editor made his additions or if he may have been trained in a different region.
Richley