Unless you have kidney/renal problems or history of stones, Vitamin C at high doses (up to bowel tolerance) may potentially be theraputic like you put it. I believe they've tested Vitamin C on rats at ~12 grams per Kg and it killed them. 12 grams of C per Kg for a person weighing 150~ lbs (~70Kg) is a little over 800 grams of C that is potentially lethal. But... each individual is different. Most research states that the body only holds 200MG of C at any given moment with good control mechanisms the oral route. There's also the potential for C to block copper absorption, but improve iron absoption.
I can't imagine anyone taking 100GMs of C in a single dose. Maybe it was broken up in 10GM doses every hour, but the source you've posted does not elaborate how the person took the 100GMs.
It more than likely depends on the individual how much C is tolerable. A concrete recommendation is not a valid way to explain that allergies will end or symtoms will not appear at such-and-such dose of Vitamin C. Many people trial-and-error until C doses hit bowel intolerance, then decrease a gram to prevent it.
Here's an oldie, but interesting read:
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