that's not quite so, that's the problem, can't have 6th princess without first to fifth there, and line for throne in royalty are not named for the numbered heir, and even in royalty and nobility, the terms are gender heavy, take for example a royal/noble family have 3 heirs, the first born being son, the second born being son and the third born being daughter, the first born will called the eldest son, the second born will be called the youngest son and the third born will be called the eldest daughter, she will not be called the youngest daughter just because she's the youngest born, but the eldest daughter instead because she hath no little sister, thus in royalty they will each refer as the first prince, the second prince and the first princess