It can happen and has been known to. best practice is to attach a piece of tape to upper corner of tank with 60 days/Date written on it from time of install and prepare to change.
While some things binding to GAC will be mostly a one way ticket (e.g., permanently stuck), many things bind reversibly and can be displaced if something else comes along that binds more strongly and displaces it. That might happen well before the whole batch of the GAC is depleted/occupied, so don't think of it like a process that only happens after a long while.
Think of the whole process as an evolving equilibrium of what is bound to the GAC.