It has been stated from several sources that Stern has the capacity to make 50 pins/day. Assuming there is some down time for parts issues and constantly switching from making 500 of this and 1000 that, lets say the number is 30/day.
52 weeks in a year, but with holidays, I guess that would be 50 work weeks, and I don't think they manufacture on weekends.
50weeks x 5days x 30pins = would be 7500 new pins per year shipped by Stern, with a potential for >12k pins a year.
some factory tour images:
https://pinballnirvana.com/forums/index.php?threads/pinball-expo-2018-thursday.14030/