Ok, I read too fast, and misread your post.
Notice my post referred to "Tendonitis," and you refer to Tendonosis.
There is a big difference, and yes, tendonosis is degenerative and usually the result of a long term chronic problem.
However, 9 months can be considered chronic, and I still believe it is a result of the change in walking pattern due to the orthotics.
thanks Edward. the only reason I became unsure was this: Tendonosis refers to degeneration of the achilles tendon, which I presume may have taken longer. Of course, I need to be sure the guy who interpreted the MRI didn't end up using the wrong term.
Since this new issue started after the orthotics, I would say it's new. However, plantar fasciitis can take a very long time to calm down. Also, a tendonitis can take as much as a year to calm down, and that's with regular treatment.