Are we sure Harry being Starborn was planned?  I don't remember anything specific in the books or WOJ saying that.  However, I am sure I am probably wrong considering it is taken as gospel around here.  I was thinking that maybe all this hoopla around Harry being starborn isn't because they planned it but because it just happened.  Maybe the "key" ingredient is that he was born while his mother was killed by outsider enhanced magic.  Not just that she was killed by magic during his birth but that part of the catalyst of his birth was energy from "outside".  The reason Starborn are so rare is that outsider magic isn't used on women in the process of delivery very often.

The reason Elaine is a "candidate" is because her mother died during childbirth.  Maybe even by magic.  She is described as candidate and not a starborn because they don't know if OUTSIDER magic is envolved.