whats the certification testing? do they test up to 60degs or only up to 30degs?
Ah yes, well.
The reality is that the wording in the certification standards over spinning is so vague and minimal that it really comes down to the professionalism of the flight test team, and what they consider an appropriate level of testing.
I would always ensure a significant amount of mishandling, and a variety of spin entries - but some manufacturers do the absolute minimum, and the authorities sometimes let them get away with it. What was going on between FAA and Cessna in the 60s of course, is anybody's guess - Cessna wouldn't tell, and anybody who worked on it will have retired long ago, and in all likelihood are using another form of aerial conveyance by now.
Which basically means, nobody has a clue.
G