Interesting. Assuming SA numbers started at 0000, 100, or 1000 in 1977, that s/ns were sequential, and bearing in mind that the SE90 was only briefly produced 1989-91, that suggests around 40,000 rifles over 23ish years, so an average annual production rate of around 2,000 - though I imagine a fair bit more in the 70s through mid-80s, and tailing off quickly after new fixed-barrel rifles like the HW77 - and eventually the TX - appeared on the market.