I'm not sure this will help you much because there is nothing official about it. But, I have developed a personal data base over a number of years for the Safety Hammerless revolvers. I have several hundred shipping dates for both the 32 and 38 Safeties. The last 32 Safety Hammerless that I have listed as shipping before 1890 is number 6560 which shipped in December of 1889. The 38 serial number list is not as clear cut. The last normal gun that is listed is # 28889 which shipped in September of 1889. The first gun shipped in August of 1890 was Number 37938. I would probably assume that any 38 before 30000 would be pre 1890. I hope this helps.
Mark

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Mark Connot