IEP Question

How long is an IEP good for? What I mean is that I am aware that it is reviewed annually to make sure that goals are being met and that every three years, the child is re-evaluated but my question is if the annual review shows that all previous goals have been met, do we just set new ones each year until the evaluation or once the goals have been met is the IEP null and void? I was just curious because with Julia's IEP it would seem to me that if she met all the goals that we have set, then she would be good and caught up with the crowd and that there wouldn't be any more goal setting needed. If this is the case, would she still be re-evaluated in three years or not?

Does anyone know how exactly this works?