Early on, my own tolerance did ramp up in a series of plateaus much like your own seems to be doing. It's leveled off at about 15-20 grams per day. I could probably go a little higher if I chose a more frequent dosing schedule, rather than the 3-5 grams 3-5 times per day I'm dosing now.
I can't give any scientific explanation for that racheting-up like effect of tolerance early on except to reiterate Pauling's own conclusion as I understand it that our bodies become less miserly, so to speak, in their metabolism of ascorbate when large supplies are present.
In one of the Dr. Cathcart videos that Owen has on this site at
http://vitamincfoundation.org/videos/, Cathcart does mention the phenomenon of increasing bowel tolerance over the long term. He attributes this to the extra oxidative burden carried by the body over time in the form of "gremlins" like chronic low-level inflammations and infections. One such infection that is almost pandemic and often unnoticed or uncared for I think is gum disease/gingivitis.
Cathcart also writes in his
http://www.orthomed.com/titrate.htm:
There is a certain dependency on ascorbic acid that a patient acquires over a long period of time when he takes large maintenance doses. Apparently, certain metabolic reactions are facilitated by large amounts of ascorbate and if the substance is suddenly withdrawn, certain problems result such as a cold, return of allergy, fatigue, etc. Mostly, these problems are a return of problems the patient had before taking the ascorbic acid. Patients have by this time become so adjusted to feeling better that they refuse to go without ascorbic acid. Patients do not seem to acquire this dependency in the short time they take doses to bowel tolerance to treat an acute disease. Maintenance doses of 4 grams per day do not seem to create a noticeable dependency. The majority of patients who take over 10-15 grams of ascorbic acid per day probably have certain metabolic needs for ascorbate which exceed the universal human species need. Patients with chronic allergies often take large maintenance doses.
The major problem feared by patients benefiting from these large maintenance doses of ascorbic acid is that they may be forced into a position where their body is deprived of ascorbate during a period of great stress such as emergency hospitalization. Physicians should recognize the consequences of suddenly withdrawing ascorbate under these circumstances and be prepared to meet these increased metabolic needs for ascorbate in even an unconscious patient. These consequences of ascorbate depletion which may include shock, heart attack, phlebitis, pneumonia, allergic reactions, increased susceptibility to infection, etc., may be averted only by ascorbate. Patients unable to take large oral doses should be given intravenous ascorbate. All hospitals should have supplies of large amounts of ascorbate for intravenous use to meet this need. The millions of people taking ascorbic acid makes this an urgent priority. Patients should carry warnings of these needs in a card prominently displayed in their wallets or have a Medic Alert type bracelet engraved with this warning.
Perhaps I should get one of those medic-alert bracelets that says "ascorbate freak" on it or something more clinical sounding.