As a general observation an inverted spin will not happen in your typical GA trainer
maybe not but you then go on to quote the aerobat in a cocked up aerobatic manoeuvre, and many aerobatic aircraft (maybe not so much the aerobat) WILL get into an inverted spin from a botched manoeuvre, the most likely I have found (and how it happened to me) is going for a vertical roll into a stall turn, stick goes forward to keep vertical and you the put rudder in possibly against aileron and off you go.
You then say this should not be discussed in ab initio, unfortunately there are pilots that will try aeros without proper training, these are the ones most likely to mess it up and at least if it is discussed then they have some idea how to recover - also it is not a bad thing if they then go on to aeros to already know the principle, after all it is not that hard to teach - opposite rudder, stick progressively back OR forward until the spin stops! (Obviously just concentrating here on how little change you need to make rather than going through full spin recovery detail)