That is correct.
> What happens if you cut off the data at 2022, 2021, 2020, 2019, 2018, etc and plotted those graphs? You'd see a different (rather than merely truncated) graph, no? Maybe even a different trend. So if my understanding is right, this is a pretty wiggly metric. The history of something you want to use as a historical trend line should not change as you append more data.
I see your point, but I don't see how it is avoidable. From my knowledge, any user churn metric will suffer the same effect: If you consider a user is churned after two weeks of inactivity, then this will change if you change the cut-off (the last two weeks of the this month? the two weeks before them? ...etc).
Even if you measure the "elabsed time" instead of "last seen", the cut-off will change your curve.
Extreme example: If you assume a user is churned after 1 year of inactivity (elapsed time since last activitiy), then a user that shared one story in 2007, and then a second story in end of 2023, will apear as active. If you change the cut-off from 2023 to 2022, then the user will appear as inactive.