When I did my PPL decades ago, spins were mandatory. We used C150s back then, and it was very difficult to get them to spin properly. I suspect that most C150 / 152 'spins' entered from the classic 'one knot per second' deceleration method are really semi-stalled spiral dives, hence the ease of recovery.
One very experienced instructor (ex-WW2 ex-Spitfire and ex-V bomber pilot) I flew with would use a deliberate flick entry into the spin, with the aeroplane rolling 'over the top' inverted and dropping into a spin as pro-spin controls were held. I recall these entries led to 'proper' spins in that they required the 'full opposite rudder, stick forward' spin recovery. But they did recover OK, not at all as MJ experienced.
Several decades of Chippying never led to any nasty spin experiences despite that aeroplane, at least in the early days, having a bit of a reputation in that department.
The Yak52 loved to spin and would do so at any opportunity. Flat spins off a botched stall turn being one of its party pieces. Recovery from flat spins (which I practiced with none other that Genna) required instant opposite rudder, full forward stick, and in-spin aileron. But recovery was fairly quick and reliable if you did it correctly (rotation in the spin was nose-high and fast).
I agree with Ghengis, however. Having done very many spins over the decades in many aeroplanes, only sometimes with a parachute, I was always aware that each was 'a bit different', and a nasty surprise might be around the corner. I also suspect that normally benign aircraft such as the C152 which are normally difficult to spin might be the very worst types to recover in very rare spin modes. I have no personal experience of that as MJ has..... It's just a feeling born of general spinning experience.
I think Ghengis is right about wearing a parachute for deliberate spinning (and of course ensuring there is the height to use it if recovery goes pear-shaped). We often didn't in the slightly more cavalier days of the 70s, 80s, and 90s (and in a biennial a few years ago we did a 5-turn Chipmunk spin without chutes) but nearly all of us got away with it. Some didn't.