My dad previously had the non-platinum version and called to cancel the card. He was then offered to upgrade to the platinum card and was told he would receive the bonus points as well. He took up the offer, made the spend and got the points.
Wasn't sure if it was only because he called to cancel but when I read the T&Cs, like you, I also thought you would be eligible as long as you didn't have the platinum previously. This was over a year ago though.