The book that I've read is simply entitled "Keraton Ngayogyakarta Hadiningrat", or something like that. I don't have the book with me now. It was published in Indonesia, in English. Those of you staying in or near Singapore can head to the National Library near Bugis Street, S.E.A. studies reference section. Sorry, you can't borrow it, so you'll have to read it there.
I think everyone has brought up valid points for consideration. We don't have to agree with each other, but we should recognize the differences in interpretation of what a "kraton keris" could mean.
So what this could mean to us collectors is that when we purchase a keris described as such, dig further and find out what the seller meant, and make a judgement for yourself whether it is believable or not.
At any rate, like I (and some other collectors) always say - buy the keris, not the story, and no matter if it's a new keris or old keris, always buy quality kerises.
And please don't stop discussing here!