I maintain an extensive collection of Winchester paper and a seperate collection of Model 21 paper of which I believ I have every paper on the Model 21 shotgun.
I conducted an extensive review yesterday and no where is 'SKEET Grade' refered to.



The above is from a Winchester issue 'Your gun for SKEET' dated 1933 and references the SKEET gun and Tournament, Trap and Custom Built Grades. I think it safe to assume that what Schwing refers to as 'SKEET Grade' is what most of us call a 'SKEET' gun and so marked on the floorplate.
In any event, the SKEET Model 21 with Sk1 and Sk2 chokes in any Grade is one of the most useful of all Model 21's.-Dick