Timothy Ferguson's Games from Folktales #42 asks where do magi get context for written material. To his answers, I will add:
A: Correspondence. Magi are literate and there is a mail system - some magi seem to think mail is the only service Redcaps perform - and IOS we assume a regular slow conversation among correspondents. I'm thinking about introducing a Correspondence score to reflect a mage's social information network. Among subjects chatted about, I suspect there's a lot of "I just read this well-glossed book by Exemplus on Subject."
B: Expert Recommendations. There are a few covenants that either produce books or have booksellers. Barcelona Covenant, for example, has among its members Carles of the Eye, a magus bookseller. I've also introduced a covenant in Toledo that translates works from Arabic, including both classical and magical works, and sorts the good magical works from the dross. Recently a magus traveling about (seeking Ptolemy's Geography) has engaged experts to suggest and arrange copies of works they think a growing covenant should have in its library.
Both of these methods have the ordinary problem of bias, but that's par for the course.
C: Snap judgement. The first of these works have already arrived, and the Guernicus in the covenant promptly laid first reading claim to the Terram work by a filius of Guernicus himself. This turns out to be a fortunate choice, but it was not based on stats - it was based on House and Guernicus' reputation as a Terram expert.