Originally Posted by
FlytheTail
No, they will not clear Y to F, nor will they upgrade J to F to free up space for Y to J. The agent probably checked J and F inventory to see if anyone in J had requested upgrade to F, which could have opened up J for Y upgrades.
Of course other things can happen during IRROPs, but even then, double upgrades are extremely unlikely.
For normal upgrade requests, they won't.
In case of oversell, they will move, if space is available, J->F, and then Y->J (cabin roll) to accommodate as many Y passengers as possible.
But as you said, in either case -- double upgrade is extremely unlikely.