Not sure if I read from his book or if Robert Cheeke (Vegan Bodybuilder) mentioned in a talk that you should take 30% off the protein count with soy products.

I know that when you look at amino acid in something, you only get what the lowest amino is, so if one is short all the rest become shortened to match it. So if say something like a veggie burger says 20g protein do you actually get 20.

Also of interest is that the only way to get more vitamin C is from an injection, otherwise your vitamin C absorption will only match your vitamin levels, so taking extra C orally is a waste.