I think its obvious that he was not born at the tower of joy...such a small structure would be a poor place to hide a pregnant woman...the text only supports that neds men fought and killed the kingsguard at the tower amd only two left...ned and reed..furthermore it seems obvious that rhaegar and arthur would choose the comforts of the dayne family seat...if we accept that jon must have been born in starfall, ostensibly under dayne care, how does that change your view of jons parentage?