Factory production barrels are distinguishable up to a point by how they are marked, when a configuration/cartridge was added to TC's advertising, and as I said special or short run (mostly for the TCA, other than the very first made by TC that were only made approximately the first few months supposedly). So presumed when, not actual start and stop dates necessarily. Kind of like the "lists" of barrel twists commonly seen, they are not all inclusive of all the twists TC may have used for a particular cartridge/length during it's entire run. Some are known variations, some just turn up. Ditto the various open sight vintages, and etc, etc, etc.
