Vlad, Thanks for your question. The serial number on Mir camera started from "20.000" not from single "00001". Don't as k me why, but this seems to be the truth. At least 3 productional Mir versions are known nowadays. So, first type started with serial #592xxxx, 2nd type with #594xxx, and the last one - from #596xxxx. All the numbers are approximate, but they fit my database records.
It's hard to say how much earliest Mir copies were released - so far I know have met only two of them ...