[snbush67]

Unless the piston was severely damaged it would not be necessary to replace it, simply being nicked by a valve would not cause concern to me.

Probably no damage to the head valve seats either, if there was it could of easily been repaired simply when lapping in the new valves.

Unless a significant chunk of metal had been removed from the damaged piston it would not effect compression.

The truth is told by way of a compression test or a leak-down test by a trusted, competent, recommended mechanic, they can also look at the inside of the cylinder and check your piston for damage.

What causes you to be curious, does your engine feel under-powered or is it hard to tune?