It does sound like a lot of this well documented knowledge on type has been lost in history with it being past down haphazardly by knowledgeable aerobatic instructors. I never taught aerobatics and spin training was part of my instructor rating and can not remember at any point having these discussions. Which is why I'm trying to prolong this discussion so others can share more information like djpil has provided.
I'm in 100% agreement with the 'know your type' mantra, but this is beyond what I consider normally available knowledge for the type. The POH recovery technique does not go into details such as djpil has provided and it's clear there's a few little tricks that can be employed in addition to the POH list that can be thrown in.
The ATSB statement that pilots should seek additional instruction as per Cessnas' advice is very pertinent in regard to these aircraft, or any aircraft you should intend to spin, even if its a variation of a familiar type.
As an aside, is it required for the spin recovery technique to be placarded in such aircraft?
I think a lot of this is still around today from what I've heard over the years regarding recoveries in 150/152s...
“Detailed investigation by the FAA, however, disclosed that problems were related to operational vagaries or anomalies, inadequate knowledge regarding the precise spin recovery procedures for the aeroplane, improper application or misapplication of recovery controls, apprehension, and confusion."
As far as required spin training during a normal syllabus. I don't see much point unless the student intends to do aerobatics, instruct or possibly some other edge of envelope type flying. A lot of stall accidents occur at a height that spin recovery would be effected too late anyway, and avoidance of the situation is the best cure, rather than recovery. Practice of low speed flight and awareness of the dangers is the key, how to stop a spin from developing in the first place is the most important knowledge.