>Basically, the constellation's effect on the night sky is proportional to the number of launches in the last month, not the total number in orbit.

For what it's worth, in order for the constellation to reach steady state the number of launches in the last month will need to be proportional to the total # of orbit. So if the constellation has 42,000 satellites and the satellites last 10 years on average (IMO that's an optimistic lifespan), you need to launch around 350/month just to maintain the size of the constellation.