The mount thoretically could have been done is just a couple of days after the kill. The skull could have been cleaned and dry in a very short time. Beetles and borax do wonderfull things.

Hides can be tanned in less than a week. Perhaps the taxidermist used a cape he had on hand. It happens all the time. My brother sold several Illinois capes to a guy in PA who used them when a guy brought in a buck that was shot up or had it's throat or jaw cut.

Putting the mount together takes just a day or two after everything is on hand and ready.