There were only about 40,000 Model 1892 rifles and carbines were chambered in .25-20, about 4% of total Model 1982 production. It was a standard offering from 1895 until the end of production, but it was never very popular. The only caliber that is less common is .218 Bee and that's due to it being introduced in 1938, only a few years before Model 1892 production was phased out during WWII.
In general, about 66% of the Model 1892s produced were rifles and that's fairly evenly split by caliber as well, so there were probably around 26,000 rifles chambered for .25-20.
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I agree a saddle ring could have been special ordered on a 24" rifle, but it would be a very uncommon and rare special order. It may also have been added later, and without a letter verifying it was ordered that way, the assumption will be made that it was added later.
In that regard, all Model 1892s with a saddle ring used a U shaped double staple style stud. The screw in stud found on most other Winchesters was never used on the Model 1892, so if it's got a screw in stud, it's been added after it left the factory.