We wait until an artificial pathogen has killed 1 million people worldwide. Then we use our best guess of which country it originated from, and resolve that country to YES.

Any release counts, as long as it had gain-of-function done to it, or had artificial gene tweaks, or some other deliberate alteration. We won't distinguish between military, private, research, deliberate, or accidental releases -- any would count

We must be confident it was unnatural in origin. So e.g. Covid would probably not meet that criteria (yet). There are suspicions, but the evidence doesn't clearly point there (so far).