Company starts enforcing upgrades -> FO gets a waiver from the company to stay an FO because he "lost and can't hold" a first class medical -> Company approves said waiver -> time to flow approaches -> Divine Intervention, said pilot can now hold a first class medical!.

Sorry, I don't believe in coincidences like that.

They hog the super sweet day trip lines so no-one else can get them, and everyone knows they are full of sh*t with their "medical issues" or whatever excuse they have used to avoid upgrading.