Don't forget Northolt...
Well, I did - but I won't now.
I was based at JFK for three years and it was not unusual for them to be using three runways at once.
For example, landings on 22L, take-offs on 22R and landings on 13L.
Yep - that has factored into internal conflicts at JFK (last-minute GA on 4L/R conflicting with climbouts on one of the 13s). And for all I know LGA was doing something similar this day (landing 4, TO 13). Exactly the kind of "other considerations" I wanted to leave room for.