Alert generation in AML and CDD 8.3 is governed by the VI 10.8 Scenario Admin. Scenario flows generate alerting events, that role up into alerts. There is typically only one alert per actionable entity per Domain. The flow, including the summary scenario, will only create an alert if the alerts does not already exists and conditions stipulated in the flow are met. If an alert already exists, it is more a question if the alert gets re-activated, i.e. a new alert version being created.
There are few limitations to the logic one can include in the summary scenario. The way you describe your use case seems something that can either be set as conditions in the summary scenario or by executing some of that business logic in the prep tables.
If you feel this does not answer your question, feel free to reach to me directly (maarten.van.dijck@sas.com) so that we can address any specific questions you're encountering.