Couple of threads I've been involved in recently have danced around this central question. Seems as if there is a large camp of people who believe there is a high number of high quality tractatus available, and they seem to fault the published line for making this so. Gripes about Covenants, specifically.
We can expand this discussion about the available number of books, too. Or go off the rails into something else altogether, which doesn't happen infrequently here...
So what exactly does Covenants say about quality of Tractatus.
This line merely states that a Q11 tractatus is sound, Q14 is excellent and Q17 is legendary. Let's try and adjust things into ranges. First will go vain: Q5-Q7, adequate is Q8-Q9, sound is Q10-Q12, Excellent is Q13 to Q15, Legendary is Q16+. Q17 becomes possible only with clarifying, which involves a significant investment of vis, an additional season of time, and limits the book to being used in a magical aura, and not traded, as such. As such, I won't use +3 resonances in any of the examples. It's been suggested that skilled scribes, illuminators and bookbinders are easy to get (I don't agree with it, but I'll stipulate to it).
If I'm understanding things correctly, an average magus with a Com 0, and no Virtues which enhance writing quality should be producing: 0+3 +1 each for skilled scribe, illuminator and binder, for a base score of 6. Resonances can be added, which, if purchased can add another +1, and if adventure is undertaken to secure these resources is another +1. So, we can assume that it is a Q8 Tractatus, on average, with some considerable effort... Effort for adventure, and effort for employing or buying the services of a skilled scribe, illuminator and book binder. So this would be in that adequate range, achievable by the average magus, someone who is more interested in doing the bell curve analytics to quantify how many average magi there should be is welcome to join in.
An exceptional tractatus requires a teacher with Com 5 and Good Teacher (3 virtue points, or 1 virtue point and some rituals which raise Com and a lot of vis) He produces a tractatus of 5 (Com) +3 +3 (Good Teacher) +1 each for skilled scribe, illuminator, and book binder. And we'll go with +2 for resonances, again. for a total of 16.
Since we have the average/adequate and the exceptional teacher/legendary cases out, what's sound? Sound is someone with high Com and not a Good Teacher, or Good Teacher, but average com. We'll change the equation around a bit and let X=com+Good Teacher, so we have Q10<=X+3+3 (skilled scribe, illuminator, book binder)+2 for resonances<=Q12, leaves X to a range of 2 to 4. Which means a Com 2 or 3, no good teacher, or Com 0 or 1 + good Teacher, or Com 4, which is probably a bit more expensive than Com 0 or 1 with Good Teacher (feels like I'm missing a combination here). Such characters do exist, but how many of them are there?
I think the idea that Q11 Tractatus being commonly available is based primarily on the assumption of Q11 being the limit of tractatus that can be purchased with build points at covenant creation. Q11 tractatus, based on what I understand about the book creation process are actually really good, and require a character, NPC or PC, who is built for communicating his ideas, somehow, either through spending Characteristic points or Virtue points.
Am I missing something or did I misread the Errata as it relates to Covenants?
I have some problems with the prices of things on the chart on page 5 of Covenants. Vis stocks too cheap, sources too expensive, but I say that only to say that there are some problems, but a limit of Q11 Tractatus available doesn't say to me that Q11 tractatus are common and easily availble.