On Statistics page -> Route Stats -> Available Seat Kilometers:
Are the numbers here based on aircraft that is scheduled, or does it count aircraft with no schedule?
On Statistics page -> Aircraft Stats -> Fleet Utilization:
The same question, does it count all aircraft owned by the airline or does it count only aircraft with schedules assigned to them?
For the first, non-scheduled planes definitely don't have available seat kilometres, because they don't have any seats for sale.
For the second, I have no idea.