When there are several watchlists selected in the same rule, the rule will return the single best match out of all the watchlists.

If there are several rules that an object triggers, the rules will be combined into a single alert (for that object) – even retroactively if needed. This ensures that there are no duplicate alerts of an object for several rules.

The Outbound API behaves differently, and rules are not aggregated. Thus, several rules triggered by one object will result in several alerts. If there are multiple objects – there will be multiple alerts (even if they all trigger the same rule).