Danny,
this is a good question, one thats been gnawing on me too.
because, of course once the wood has been tempered after floor tillering or after some beginning stages on the tiller,
there is still scraping and wood removal, and it will remove much of what was "toasted" .
so ...a final fully tillered bow could actually be scraped of the tempered SURFACE....correct?
not that the heat treatment doesn't penetrate deeper into the limbs of course.