That's good to know. I'll just leave them there then and plow ahead.
When I said "didn't fit" it was more to focus on not forcing them together. The central crutch (f1a & b) was a little thick. So the tabs didn't fit into the side rails. It's something that anyone experienced wouldn't think twice about, and in fact the instructions are very good about explaining it. I mentioned it more to focus on "see, I'm not forcing parts together!". A little sanding and everything is nice and snug.