Years ago, I had a Model 21 that was marked MOD and FULL but those were neatly lined through, and it was marked IMP CYL next to the marked through MOD and marked MOD next to the marked through FULL. Model 21 experts at the time told me that was the way Winchester did it. Don't know if that was true or not, but I didn't shoot the gun all that well and it flowed down the river of commerce for 50% more than I paid for it the year before.