Have you ever contributed multiple DOffs, as the others have mentioned? There was a bug where you weren't getting leaderboard credit for all your fleet marks, but you still got them in your pool.
I have quite the discrepancy because of this.
Lucky for me, my fleet doesn't judge my worth by how much of my stuff I give them.
I was just about to jump on board with my explanation but THIS^^ just about sums it up!
Basically, if you've donated multiple DOffs in the past and before it was patched, you'll see a difference in FC's from what you currently have and to what shows on the leaderboard!
I too have the discrepancy and it's really no big deal!
And, if your fleet are that strict, (which is nonsense) and you really want that promotion, then point them to this thread and try explaining to them that you've already exceeded the requirements for the advancement in rank!