Urgh...what are the chances !

Had same thing happen with a small stone. Left a nice grove in an otherwise perfectly good rotor

No... they were on top of the rotor ! Kinda balancing on the outer edge . The width of the weights is a little narrower than the caliper housing.
What are the odds of this happening ?

The point of the thread is unlikely events happening during a resto or rebuild . So many things have happened the are unlikely !