New Finds And Some Unknown By Me

Perhaps the coin that cause the indent was above the collar and popped out not striking fully though the coin, affecting the coin/planchet instead of the coin you have?

The link I posted lists prices for varying degrees of indents. I think one like yours was around $40 asking price.

Regards some the oddities of your coin (or coins in general): some things look peculiar. I sometimes don't see how a puzzle piece might fit to explain an event but it might be more associated with linear thinking. On your indent was the other planchet round? Or damaged already? Standing on edge or lying on an angle? With things moving fast it can be hard to imagine what fully happened. But that's why we have coin detectives like Mike/coop to help piece the puzzle together. Asking questions helps the community here expand our thinking, so ask away.

Ok its far fetched but..Is it possible that debris picked up from the roller (or from somewhere) then deposted back on the sheet were it stuck there and was punched into a blank, then the upsetting mill forming the rim joggled the piece a bit loose and the strike provided the blow that set the little piece free.
Its so smooth inside its as though pressure rolled it in, and that might explain the standing rim..
Just a guess