1
If you extend the net (not that 'net!) to catch all 1st-year SP's debut'ing in the same year, the input bus chokes and crashes ... most teams do that at some point...
We were using the very strict criterion, where two rookie SP's break camp in the same rotation.
.......
Although, now that you bring it up, why the Opening Day roster should be such a huge talking point, I dunno. We fans talk about the Opening Day roster as though it were a religious event. " .... how could you even think about Hultzen in April? Make it May, at least!!"
No special reason to make such a big whoopin' deal out of April 1, as opposed to May 15. Other than our own fan over-talk-it psychologies.