Here is an example of the Counterclash on the reverse of a '69S that was showcased in Strike it Rich with Pocket Change (Allen & Potter). It comes from Jeff's (JPL6332) collection.
You can see UNIM; IB and parts of UR (from PLURIBUS); and parts of the memorial roof. This was apparently created when a foreign object (probably a scrap of metal) entered the striking chamber and initially became lodged onto the die where some of the design transferred to the object. The object became dislodged and countersunk into the die transferring the design back to the die then fell away.
I have overlays showing what appears to be what. The first colored overlay shows the orientation of the design transfer (not a clash) in blue, the coin in green, and the red area within shows the approximate size of the foreign object and what was countersunk. Below that is the countersunk areas in green overlayed onto a normal reverse followed by details.

Some of the marks under and around UN of UNUM and the memorial roof don't seem to be clash marks, they may be damage from the object striking the die or something else (lime-green arrows below). There is this weird doubling on the bottom of RIB (of PLURIBUS) which looks a little like Machine Doubling but I am thinking was caused by the original foreign object (blue-green arrows) striking the die. I have shown deep die scratches (purple arrows) WEST of EPU and a die break in the E that may or may not somehow be related (yellow arrow).
You can see UNIM; IB and parts of UR (from PLURIBUS); and parts of the memorial roof. This was apparently created when a foreign object (probably a scrap of metal) entered the striking chamber and initially became lodged onto the die where some of the design transferred to the object. The object became dislodged and countersunk into the die transferring the design back to the die then fell away.
I have overlays showing what appears to be what. The first colored overlay shows the orientation of the design transfer (not a clash) in blue, the coin in green, and the red area within shows the approximate size of the foreign object and what was countersunk. Below that is the countersunk areas in green overlayed onto a normal reverse followed by details.

Some of the marks under and around UN of UNUM and the memorial roof don't seem to be clash marks, they may be damage from the object striking the die or something else (lime-green arrows below). There is this weird doubling on the bottom of RIB (of PLURIBUS) which looks a little like Machine Doubling but I am thinking was caused by the original foreign object (blue-green arrows) striking the die. I have shown deep die scratches (purple arrows) WEST of EPU and a die break in the E that may or may not somehow be related (yellow arrow).

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