Or, phrased differently, at what Serial No. and Year, roughly, did the New Service cease to have the earlier plain 'straight' type non-Bolstered at the rear Barrel?
Sorry, Judge, but you've permuted this question so that it matches your meanings and definitions, not necessarily those of the OP. There was no mention of "commercial" New Service in the original post - you interpreted it as that. Second, the M1917 is not based on the New Service, it is a New Service. M1917's have Colt serial numbers in the Colt New Service serial number order. But if you want to continue to pick insignificant nits,A military Model 1917 is NOT a commercial New Service, even though it is based on the commercial New Service. The question was about the commercial New Service, not about the military Model 1917. The Model 1917 always had the bolster barrel so the question would not be relevant in regard to the Model 1917.