Blocking under the posts is common with hand raisings, where you don't want the bents dropping 10 inches or so as they get vertical. I believe it's acceptable from an engineering standpoint if the blocks have their grain oriented vertically. One block is left shorter than the others to accept a stub tenon on the post. They definitely should go in before the frame goes up; I don't see how it could be done otherwise without the plywood bending or even shearing through. For crane raisings, and in general, having the posts go all the way to the foundation/sill is preferable.