Searching for diverted flights

Adding on to this - when a flight is diverted you say to search for it, what’s the most reliable filter to match?

Strange the diverted flight record response doesn’t just add a field for the diverted reference ID to save on searching costs and complexity

EDIT:

2020 Thread:

FAQ:
The diverted field is a boolean; it can be true or false. If it is true, the actual_on field will indicate the diverted time. To determine the diversion airport and arrival time (if aircraft has arrived), your application will have to find the flight for that aircraft with the same origin and departure time.

Could we get some clarity here - will duplicate IDs be returned from the newest API?