Hi Kevin,
You are correct that the events search endpoint does not return past events reliably. That is because the endpoint was built for discovery purposes. Past events rank very low where the prime consideration for an event being returned is how likely it is to sell tickets.
Our API is not ideal for data science work when you are looking or past trends.
The date range parameters work irrespectively of each other. If the event satisfies the requirement for one parameter but not the other, it will still be returned.
I hope that helps clear things up.
Best,
Malina