The Coverage Overview section gives you some high level summary information on the number of flights that we were able to track. To be counted, we needed to have at least one actual gate time (departure or arrival) or the flight needed to be identified as a cancelled flight.
Track Percentage shows you what percent of the flights we had both a departure and arrival gate time or the was cancelled. Departure shows the percentage of time where we at least had a departure gate or cancellation. Arrival shows the percentage of time where we at least had a arrival gate or cancellation.
The other coverage numbers are more specific about departure, arrival, and baggage coverage. Unlike the overview, these numbers do not include cancelled flights so may look different than the numbers in the overview.