I have had this happen with a power on stall, where I am trying to counter torque/p-factor with ailerons (since I don't have rudder pedals) and then the left wing only stalls, but I have never experienced it in a power off stall. Power-off stalls are usually pretty benign, if they happen at all. I suppose a freak gust could have caused the left wing to stall although it might have just been turbulence. If the left wing does stall and you try to lift it with aileron, that increases the angle of attack of the left wing, maintains the stall, and delays the recovery. It will recover, just slower.
A properly rigged Ercoupe will not spin, and is reluctant to stall. If you do manage to stall just the left wing, it will start a spin entry, but then the nose drops (you have limited elevator so you can't stop the nose from dropping), the AOA is reduced, and the plane is flying again. You might be in a spiralling descent, but you are flying. I have tried doing everything wrong and keeping the spin, but it just refuses to stay in a spin.
When practicing power on stalls, when the left wing stalls first and drops, if I quickly reduce power and reduce the pitch to get the wing flying again and THEN apply aileron to level out, I can recover at an altitude higher than when I started the maneuver.
