Winchester had both Trap and Tournament grades for both the Model 12 and Model 21 in the pre-WW2 1930=1940 era. But a Trap grade was not 100% a true Trapshooting set-up, as to stock dims, etc. It might be possible that your M21 was rebarreled. Was the No. 5 style of engraving done at the Custom Shop, according to the Cody Letter?

"The field is the touchstone of the man"..