With just SKEET it is a Standard Grade.
Tournament Grade Skeet Gun --
Winchester Model-21, Tournament Grade, Skeet Gun, 20-Gauge, 26-inch, Vent-Rib 01 12080.jpg
Trap Grade Skeet Gun --
WINCHESTER MODEL-21, TRAP GRADE, SKEET GUN, 16-GAUGE 01 72xx.jpg
DELUXE Grade Skeet Gun --
12131 01 20-gauge, DELUXE SKEET,.jpg
I have two Model 21 Skeet Guns I have gotten letters on. The 1940/1 letter states "Grade of Wood: Regular" and "Regular Finish." The letter for the 1953 gun states "Skeet finish" and "Skeet Grade" which as I stated above was a term never used in Winchester catalogs. They are both marked SKEET on the trigger plates.