The 686 series is not usually separated by "generations"; if you look on the frame under the barrel with the cylinder out, it should be stamped MOD 686, possibly by itself or with a dash and a number. The "dash/number" is called the engineering change, and many collectors separate models in this way. If you post the three-letter prefix we can tell you about when it shipped, usually. Hope this is helpful.

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Alan
SWCA LM 2023, SWHF 220