Any question answered...

I've done a couple up with a chain whip then I guess leg power would have tightened them further if possible. And then they came undone during polo. I also stripped the lock-ring thread at the same time.

That's the trouble with using something designed for track racing on trick cycling bikes. At some point the lock ring is going to come under pressure, and once the sprocket is on the move it has a huge mechanical advantage to drive the lock ring off by shearing the threads; one or other of the equally fine pitched threads is going to have to give if you don't get your legs out of the way. The repeated high back torque involved in trick cycling tends to open up a gap for everything to go wrong into; threaded couplings will always loosen off if there some radial shaking.

Fundamentally, threaded sprockets are not actually a good design, they work just well enough when well made and used within the performance envelope envisaged by the original designer, but they are marginal and low ratio gearing or poorly matched tolerances will fuck them up. Fortunately, bolt-on sprockets are now widely available.