Astrological Mutable Supernatural Abilities and Teaching

Many companions do not have entire "truly free" seasons available to them. It's just assumed that, during the course of an entire year, they have enough time to train or teach or be taught for the equivalent two seasons (or three, if Wealthy, or one, if Poor) . It then stands to reason that the amount of teaching equivalent to a single, full time season be "spread" over the course of at least one entire year.

This seems to suggest that someone with an Astrological Mutable Supernatural Ability (say, Shapeshifter) that only works during the four mutable months of the year, could teach that Supernatural Ability for one season/year. Any ideas of why this should not be true?