Regarding The Cow and Calf Oath, I agree that the statement “…will not sell or freely give copies of that book… “ to be ambiguous. The purchased book could be considered a copy of the intellectual work, or it could be a physical good, which you are not supposed to copy. The context of what is said on p95 in the section on Excellent books regarding the Cow and Calf Oath, and what is said on p95 in the section on Sound Books, stating that the trade of equivalent sound tractatus is very common, I believe removes that ambiguity.
You seem to be saying that disallowing a secondary market would let the author make more money, so that is what authors would have The Cow and Calf Oath say. That is not good economics. If the price that people are willing to pay for a tractatus is set by supply and demand, the price that someone is willing to pay includes an evaluation of the resale value of the tractatus. If there is a non zero trade in value, the purchaser can charge more for each text, if there is no trade in value, they must charge less. Consider Xbox games or Playstation games. The only reason the manufacturer is able to charge the prices they do at the quantities that they sell is that some of those buying games plan that they will trade them in for other games at a later date. Or look at Magic the Gathering cards. Wizards of the Coast spends a great deal of time making sure that the secondary market for their cards is healthy, because they believe that having a secondary market for their cards allows them to sell more cards and thus make more money.
The Cow and the Calf has to do with monopoly power. The existence of a secondary market does not do away with monopoly power, the producer still controls how many copies of the book are in the market. Allowing someone else to produce your goods at the cost of material and labor does keep you from having monopoly power.
Now, as for what is average vis in canon. The main rule book defines low, medium and high vis campaigns. It does not define what average level of vis for a campaign. On the contrary, the rules are very explicit in saying this is a decision that varies from campaign to campaign. By saying that you are below average, I expect you mean that you have less than 10 pawns per mage per year, since that is less than what is given for a medium vis saga. My inkling is that most people play in low vis sagas (5 pawns or less per mage per year.) Whether this is true or not, doesn’t really change my point. My point, if perhaps expressed badly, is that this description of the economics of teaching large classes only works if some particular assumptions are made, and that if different assumptions are made (travel is harder, there is less communication between tribunals and covenants, there is less vis in the saga) you would have a different result. I have said this before, and I will say it again: There is nothing wrong with being in a game with your ground rules. However, when you were describing what the economics of teaching large classes would be, it seemed like you were stating that this would invariably occur in any game that used the rules as written. I just wanted to draw out those unstated assumptions, so that people could decide whether having super teachers instructing large classes would reasonably happen in their game.
As for how much vis is in canon, I worked from the 200 pawns of prizes that were offered in the Normandy Tribunal as tourney prizes, and estimated 25% of those prizes were books and items versus vis sources and then that only 1/3 of the vis sources of the tribunal were tourney prizes . That works out to 450 pawns a year, so I stated things as an assumption of 400 to 500 pawns for the whole Normandy tribunal. That is around an average of 4 pawns per mage per year. Then I figured that young mages would get less vis and more powerful mages would get more vis. The idea that older, more powerful mages hog all the vis seems reasonable to me, but YMMV. Statements about minimums are justification for junior mages getting less, not for what the average vis in the Tribunal would be.