This leaves out what happens to the C before it is excreted. It doesn't suddenly leave the blood stream and enter the urine stream when it is there in excess amounts. The body processes it.
We are all different in genetic make-up. That is why anecdotal cases are useful in statistics, which can lead to scientific study.
Extreme use of almost anything is eventually damaging. The simple obvious fact is that balance is disturbed. We have to realize that something ingested in excess at twenty can prove disastrous at fifty.
A note: Extremist in two cases, C and acidity. Each side claims they have the major answer against disease. C will cure most illnesses!
Anti-acidity cures all diseases!
C acidifies the body.
Alkaloids neutralizes (buffers) much of C.
Both have hundreds of anecdotal cases to "prove" them.
Science and statistics tell us that both are true in many cases.
BUT, scientific examination also shows that results are negative or neutral in many cases, too.
Add: If you are using massive C dosage and your urine begins to "burn" you are not reacting safely to the dosage. Your kidneys are under attack. This can result in kidney failure some years later. Take care. Lower the dosage until you do not get that burning or other uncomfortable sensations.
Research both sides of any such claims before blindly beginning use. Perhaps they will work for you, perhaps not. Learn at what point to make a final decision, and that is not before you have facts on which to base that decision.
Many of these things have years, even centuries of use to study to determine usefulness in your case. It only makes sense, to me, at least, to learn all you can about a thing that can affect your health before using it.