ArM 5 core book indicates that a teacher may be purchased by paying points according to her com + teaching + highest ability taught. It explicitly notes that multiple abilities can be taught by a teacher but gives no parameters for pricing them.

When this teacher is statted by a player as a sentient, functionally immortal forest with a teaching of 8 and 12 different abilities above 5 I became quite worried.

Given that this same formula was reprinted in Covenants without elaboration, are there useful guidelines for how many abilities a purchased teacher has at covenant creation and or alternative pricing methodologies for immortal teachers?