WRT the weighing/measuring of veggies, I try to stick to the sheet in general, but I'm not exact about it. I think that the 2 cup rule was probably established to make it easy to remember/follow. But IMO there's no "magic" to the 2 cups. After all, we've discussed several times that volume can be so different based on how we chop the veggies, whether we compress them into the cup, or whatever. Plus, we know all veggies aren't created equal in terms of carbs, calories, or any other nutrients.
While I'm a believer in the overall IP program, I'm pretty cynical about the motives behind some of the requirements - how much is science vs. convenience vs. profit.
Probably not the most popular opinion, but my 2 cents.