Kingdom Hearts Riku's Keyblade

Okay, so I was browsing some stuff on KH on the internet today, and I ran into this little article about the different kinds of keyblades in the game. Most of the stuff wasn't anything new to me, but then I got to Riku's keyblade, the dark one that he has when he's possessed by Ansem - i.e. the one used to unlock Sora's heart. It said in the article that this keyblade was created using the Princesses of Hearts's captive hearts. I didn't know that, so I came here and rewatched the cutscenes from KH1 that involves that keyblade, and it never says that that's how the keyblade was made. In fact, it never really says anything at all about where he gets it from, it just sort of appears after he gives himself to the darkness. So, I was wondering, is this information from somewhere else, like maybe KH1:FM? Or is it not true? Or what?

Here's where I read it from: http://www.khinsider.com/kingdom-hearts/weapons-11.html

 

If you watch it agine you'll see that when Sora uses the blades power to free Kairi's heart other hearts re enter the other princess bodys and the blade disaperes. The only reason Hearts other than sora and Kairis would come out of the blade is because of the fact it was made of the other six's heart. Do you understand?

 

Yeah you can't get it, bro. The key disappears after Sora uses it to unlock the princess' of hearts hearts (@_@).

I actually thought it was attainable for a while too, so yeah. xD