At the moment I checked, the employee site should be accurate since it uses bookings. Admittedly, the number in each cabin depends on seat assignments for elites upgrading and paid Y/B fare passengers - before an upgrade goes through or the Y/B fare upgrade is processed they'd be included in the coach total and afterwards in the FC total. But paid FC would show in the FC total even if they didn't have a seat assignment.

As always, FC may fill up if they're holding those open FC seats for sale and turn them loose later since some of the coach passengers could still be upgraded.

Jim