What you are hearing is mostly right. But FDX does bids differently than most are used to.

It may appear upgrades are occurring at a blistering pace as newhires in training are awarded widebody seats. But the training dates assigned are 12-18 months in the future. As you can imagine any training date over 3 months away is subject to change. Many go to training earlier or later than what is initially posted. Sometimes the the sum of the updates means training several months later than planned.

But they are, mostly, accomplished in seniority order. If training is done out of order a crewmember gets passover pay (POP) until it's made right. It gets complicated when there is training from two or three bids still in progress. POP only applies to the bid you obtained your award or later bids. Management sometimes complains about being overwhelmed by training order issues. Errors are not unusual. If they would only do short bids their passover queries/problems would disappear very quickly. But this is unlikely to happen as POP is used as a tool to maintain the instructor corps.