Where are you coming up with 13? Between the July and August bid packs, the number of captains changed by 9. Two were retirements. One was a resignation. The rest are still on the seniority list and will likely return at some point.

Of the 7 FOs, one was a retirement and one chose to leave after a second unsuccessful upgrade attempt, leaving five who have moved on to whatever, which is actually slightly below the monthly average so far this year.

None of this has anything to do with "vague upgrade behavior". One of the 5 FOs who resigned had already bypassed multiple opportunities to upgrade. Nearly everyone who takes a job at an ACMI carrier is doing it as a stepping stone to somewhere else, so in an environment where major airlines are sucking up anybody with a hint of 121 experience, let's stop acting as if the high turnover is somehow unique to ABX.