For Glasairs, the situation is straightforward.
The POH states clearly that it was designed as a sport aerobatic aircraft, including steady inverted flight if the optional flop flop tube is fitted in the aux fuel tank, and the specified inverted oil sytem is used for the Lyc. engines.
This does not apply when the optional wing tip extensions are fitted, which greatly reduce roll rate, and are not stressed for aeros.
Some, particularly Glasair IIIs, have been used for delightful professional displays in the US.
In an early Glasair News, there was a long article on spin testing by a skilled aerobatic pilot. The essence of which was
(a) very difficult to get into a spin using normal tequniques. It would drop into a spiral, but having found a technique
(b) normal recovery worked quickly, but was easy to push the stick too far forward, and they recommended full opposite rudder and letting the stick go!
Glasair have made it clear that the reason that they prohibit intentional spins is the US comensation environment. Commercially, they were not prepared to spin test an envelope of possible assembly errors by amateur kit builders. Eg, who knows the effect on spin recovery of someone locating the tailplane 1/2" either forwards or aft of that specified, which would be unnoticed in normal flight.
Several years ago, someone was trying to get CAA approval for aeros for a GIII, all of which are on CAA permit, being outside the remit of the PFA. I do not know if that was successful.
Mike.