This is a subtle issue to which my troupe has given a lot of thought in the past, in part because of a merchant-minded PC Redcap and the Exceptional Book Boon. The short answer is: what happens depends a lot on a) the type of book one is looking at and b) a number of "environmental" assumptions one might make about the Order at large - but by and large the demand for book copies is far lower than one might expect at first glance.
I'll note in passing that books that can be written by mundanes, including books on arcane subjects such as Finesse, would have their own dynamics (they'd be easier to create on the cheap, but then, a mundane instructor is better than most books anyways). I won't even touch books on Parma, books with limited public such as books on Spell Mastery or esoteric abilities, or Lab Texts. Instead, I'll just focus on Summae and Tractatus on a generic Art. These need to be addressed separately, starting with Tractatus.
First of all, remember that the Order in 1220 has a roughly stable population about 1200 members, each active on average about 120 years after Gauntlet. In other words, it "renews" itself at a rate of about 10 magi/year who must relearn the lessons of the previous generation. Changing these numbers or later ones a little won't change the end result by much.
Now, suppose you have written the best Tractatus ever written on Corpus. I'd say only a magus out of 2 advances in any particular Art beyond the point were good Summae (at least as good Quality as your Tractatus) are sufficient, as one cannot specialize in more than a few Arts. Of those specialists, maybe 80% would want to study your Tractatus (the rest prefer to study from vis or Djinni; or they may dislike you, your House, or books not written in Greek; etc.). So, on average 4 magi every year, i.e. 1/season. Meaning that if logistics were perfect, a single perfect copy of your exceptional Tractatus, bound in resonant materials (see Covenants) and briskly traded would suffice for the whole Order.
Now, that won't happen. Logistics are not perfect, and there will be a boom of interest in the first decade after your book appears. But it does show that even a very "globalized" Order only requires a handful of copies of any given Tractatus that pass from hand to hand via sale, loans, hospitality etc.. Note that a very fragmented, insular Order works effectively as a collection of independent smaller communities, each of which then requires even fewer copies of any given Tractatus. And while any mundane can copy a Tractatus, it does require significant effort to make it resonant (particularly beyond +1) further pushing towards a smaller number of higher-Quality copies circulating more frequently. Finally, the above is about truly exceptional Tractatus; merely "good" ones will see lower demand and thus fewer copies (the same would be true of Commentarii, that have a restricted audience because it needs to have read the base Summa first).
Now, if you are not only an excellent writer, but a senior specialist in Corpus and, many decades after your Gauntlet, you write the next Branch of the Arts, the best Summa the Order knows on Corpus, the situation will be different. More magi will want to read it (and its reputation will spread further); reading it will require several reasons; and many covenants will want to have it as a status symbol. You will make a small fortune selling access it, at least a queen of vis over several decades, but that probably pales in comparison with all the prestige and networking opportunities it will bring (note in this sense that Exceptional Book in Covenants is an External Relations Boon rather than a Resources one). And I would not find it unbalancing, either for game play (a senior magus leveraging his specialty, be it dragon-hunting or enchantment, is supposed to have a similar impact), or for setting balance.