Sorry to be so late, but just realized that I have a box of 1950s 16g Federal "Monark Skeet Shells" with the red sweater trap shooter on the front. The top flap is clearly stamped "SECONDS", as are both of the inside flaps and both sides of the box.
I had not considered the possibility that this had been the "second" loading for the hulls?
BUT the shells inside are "Red Head Long Range" with "Maximum 6 Load" on the top card wad. Maybe it's the "second" loading of the box??

https://sites.google.com/a/damascusknowledge.com/www/home