In the July 1931 Winchester catalog the Model 21 was only offered in Standard Grade.
In the November 1932 Winchester catalog, after being acquired by the Olins at the end of 1931, the Model 21 was offered in Standard Grade (stock and forearm of standard grade walnut), the Tournament Grade (selected fancy grain walnut) and the Trap Grade (fine figured grain specially selected walnut). All three grades made in all three gauges. Also, 12-gauge Tournament and Trap Grades could be had with 32-inch ventilated rib barrels.
The 1933 Winchester catalog adds the Custom Built Grade in all three gauges with stocks said to be "specially selected fine figured fancy walnut." Also, the Model 21 Skeet Gun was added, offered in Tournament, Trap and Custom Built Grades.
By the 1934 Winchester catalog the vent rib 12-gauges were offered in 30- and 32-inch.
In the 1935 pocket catalog the Trap Grade Model 21 Skeet Gun with pistol grip stock is shown with checkered stock cheeks.
By the 1936 pocket catalog the Tournament Grade is gone and all the Trap Grades are shown with checkered stock cheeks.
1937 and 1938 pretty much the same.
By the 1939 catalogs the Trap Grade (all three gauges) is phasing out, replaced by the Trap Gun in 12-gauge only. Ventilated ribs are available on the 26-inch barrel Skeet Guns in all three gauges. The same in 1940.
The January 2, 1941, Winchester catalog adds the Model 21 Duck Gun.
By the 1948 Winchester catalog 28-inch ventilated rib barrels became available and 28-inch was now the standard length for the Model 21 Skeet Gun. Also the Trap Gun is shown without checkered stock cheeks.
The big 1950 Winchester catalog again shows the Model 21 Trap Gun with checkered stock cheeks.
What disconnect there may or may not have been between what the folks on the factory floor were doing and what the folks in the office were stating in the catalog is a whole other question.
