Even though all manufacturing was moved to Huntsville in March of 2015, frames marked Charlotte were still being used up through December 2016 in Huntsville. The first frames marked Huntsville start in January 2017. All Smoke models are indeed made in Huntsville as they were introduced in September 2017. Also, just because an R51 is marked Charlotte does not make it a G1. G1s had a couple identifiers: R51 logo on the slide is in a different location and the sights do not have set screws.I think that you are right that at the end of the production run they started using any and all extra parts to assemble guns and get them out the door. I also think that your pistol could very well be the factory prototype model for the "Smoke" color variation. This could explain the out of sequence serial number, blemish and used status. Either way, it is going to be difficult to verify any information on the gun now.
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