I've got Through the Aegis in front of me (just got it today). I'm looking at the Mundane Knowledge section for the Northern Sea. It doesn't look like the texts have the blanket +3 for Mundane texts called for from Covenants.
The core book set text quality as a base of Communications +6. Covenants changed this to Communications +3 +(up to three for book construction) + (up to an addition three for resonance). To compensate for the lack of resonance, mundane tomes (but not Arcane abilities) were increased to Communications +9.
Given that the explanation is in a text box, I think everyone assumed that texts had been changed to Com + construction + resonance (no +3), decided it was an annoying nerf and a record keeping hassle, and just defaulted back to core.
This got me to thinking, if the average Summa has a default quality of Com + 8, the much-maligned text qualities in covenants make sense. Art score 36 + 2 Com = Level 15, Q 13 Summa, at the low end of the sound range. I'm also flipping through Through the Aegis and not seeing any magi with virtues (or flaws) gained in twilight. Looking at third edition, enhanced ability to write about magic is a classic twilight benefit. This would suggest that, at some point early in the edition, it may have been assumed that more magi would have Good Teacher then ended up with it. (Though perhaps not many. The number of situations where magi can pick up seven warping points are somewhat rare).