This seems like a pretty good place to promote the elimination of the SP/MR labels completely
. They should be roles, but any pitcher should be able to have the endurance to start if you let them (just not necessarily the effectiveness). Pitchers very rarely get drafted as relievers, I would guess 90% or so of the MLB pitchers were starters through a large portion of their minor league career.
This has been discussed at length (along with other pitcher issues)
here.