An encyclopedia of weirdness

Yes, Sam got the amulet from Bobby who told him that it was 'real special'. He got it as a present for John, but gave it to Dean instead. I think it's fair to say that Bobby would have had no idea about its 'properties' simply because angels hadn't been to earth for 2000 years to that point, I don't see how he could have known of such a very specific and unlikely function for the amulet. :) But it's a classical retcon, no doubt about it and it bothers me, because it fires all kinds of speculations about John being the intended target as the 'righteous man' who breaks the first seal etc. I just fnd that notion ridiculous and it doesn't track back very well. I also dislike the whole 'it was all predestined' notion that comes with this retcon. /sigh