Do summae have a maximum quality capped by their level?
For instance suppose you had an individual who had Communication 3 and the Good Teacher Virtue and Second Sight 8.
Obviously, he could write a summae on Second Sight of Level 4, with a quality of 12.
He could drop the level of the summae to Level 3 to gain a quality of 15.
Can he drop the level of the summae to Level 1 to gain a quality of 21? With a score of 21, an apprentice who has just had his arts opened but has no other Supernatural Abilities, this would provide 6 XP in Second Sight, of which the apprentice could only keep 5, but would still be enough to allow him to learn Second Sight .
No. However, lowering the Level can no more than double their Quality. Following your example, a character with Communication 3 and Good Teacher can write a Summa of Quality at most 12x2=24 (by lowering its Level by 12/3=4, if the topic is an Ability).
If the aforementioned character had Second Sight 8, he could certainly write a L1, Q21 Summa on Second Sight. However it would not be a very useful book: characters who already know Second Sight necessarily have a score of 1 or more (so they can learn nothing from such a book), and characters who don't know Second Sight can't learn it from a book (see below).
For a Gifted character to learn Supernatural Abilities without the appropriate Virtue, someone with the Ability must Teach or Train him (Arm5, p.166). A book won't do, in general (Ars Notoria from RoP:D is an exception).
Incidentally, note that to learn a Supernatural Ability by Teaching or Training, one must gain a score of at least 1 during the first season - but nothing says that a higher score can't be gained. In your example, if the (Teaching or Training) Source Quality were 21, the apprentice would keep all 6xp, for a final score of 1(1).
Note it should be easier to just teach the student Second Sight BEFORE you open the Gift, then Open the Arts. You'd only need a InVi lab total of 25, which anybody taking an apprentice should be able to manage.
Actually, I screwed up the math - I was thinking 5x the XP. It's 5 times the score in the Ability, minimum 10 for a Minor Virtue, so you need a 10 to destroy, a 20 to preserve if the Ability is a 1-2.
To address the OP - If you wanted to, you could have a L1/Q25 book - however, by RAW, you can have only one source of XP/season, so there's little point to have those extra 20 points. I do think the actual quality limit would still be whatever the max for summae is - 30? 35? (sum of level + quality no greater than 35?). Noble's parma. The books are literally right behind me, but I don't want to be bothered to look it up.
HOWEVER - it's a reasonable interpretation to say that such an activity would leave you with 4/5 of a season to occupy yourself with - as such, you could read 5 1/25 books in a season: for example, if a summa was entitled "Our world, and Our Place In it," and contained all the basic AM Lore skills (Magic/Farie/Divine/Infernal/Hermetic) at L1/Q25, then as GM I would allow someone to read that all at once.
Unfortunately, while that's IMO a reasonable interpretation, I don't think it's explicitly supported anywhere in the ruleset.