I can't find any mention of the effect of vitamin C on symptoms in this article. Surely what we really want to know is whether the treatment reduces flare-ups. It's conceivable that a treatment could inhibit the formation of urate crystals without lowering serum urate, and this is what needs to be tested. Further, the claim that "the blood levels reached a point where increasing them further was unlikely to have any extra effect" is merely an assumption.