It's not unusual to add unknown defendants to an action where all the tortfeasors are not known yet. This is simply a precautionary measure to ensure that Apple can bring a claim for damages against a party unknown to them should, through out the course of the proceedings, it is found that an unnamed defendant arises. By not adding an unknown party, would leave them in a situation where they would have to reinitiate the process from the start. As someone stated earlier it's simply a case of covering all bases.