goji - vitamin C - usda testing method?

I have been been trying to find solid evidence for some of the contents of Goji. This particular web site suggests that Vitamin C is contained in Goji but the USDA does not recognized. Here is the excerpt I'm referring to. My question is two-fold.

Does the explanation below make sense? Are there various methods for testing food for Vitamin C?
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But unfortunately, this service also creates confusion, and here’s why. The answer gets a bit technical. The USDA tests foods in coordination with the FDA. It comes down to how the USDA tests for Vitamin C, which is different from how the human body actually uses Vitamin C. The USDA test uses a chemical definition of Vitamin C that is very narrow and specific.

On the other hand, your body uses a number of related chemical compounds as though they were Vitamin C. In chemical terms, these are called “analogs.” The type of Vitamin C that’s in Goji berries is an analog of Vitamin C that doesn’t fall within the strict USDA definition of Vitamin C. But your body still recognizes it as Vitamin C and uses it as though it were Vitamin C, and it has the same effect as Vitamin C.


http://www.forgojiberries.com/

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