Only one more thing - The 1/4" - 1/2" expansion space around the edges of the room are for expansion. That's why we put down the 1/4" round moulding. It's used to, essentially, cover up the movement in the flooring. There, too, I wouldn't fill anything in.
I'm beginning to wonder about some of the subs you'ver run into. I certainly do appreciate the clarification in your Follow-up. However, these days, maybe the only type of flooring you can install w/o an expansion space is the Engineered flooring. It's designed NOT to expand and contract but I think out of habit, they still recommend a 'space' around the perimeter of the room.
Oh well, moving right along. Thanks again for clearing 'things' up.