That's odd. BCIN can absolutely do design for part 3. That's the entire purpose of the additional test and class of license. Large buildings and complex buildings allow for the design and to take responsibility for the permit application of part 3 buildings.
I was talking to some examiners at Markham yesterday and they said that a BCIN can do the design and file the permit but can't do the general review. For buildings that require the general review, the designer has to hire an architect to sign for the commitment to general review. This is insane in my mind, so someone who is qualified to design in accordance to the OBC isn't qualified to verify that the construction is per their own approved drawings?
Apparently it's to avoid lawsuits from the OAA... can't confirm that but it checks. It seems I have my answer and I hope it changes in the future.