"borderless proofs"...a worthwhile rarity?

Steve1124

Once in a blue moon, i'll find one of these "borderless proofs" available on eBay, usually at a premium price. Surely there's nothing ATTRACTIVE about them, other than their rarity. In my limited understanding of them, there was some kind of process during the production of the cards whereby there were like four color shades of the card to be made. They are the same SIZE as the final card, and so there would only be a maximum of four of these per player. I've only seen them offered for 60s cards, and am assuming these were not placed in general circulation--which only tends to enhance their rarity. It's also my understanding that PSA won't even grade these cards. Does anyone know why that is? I also very rarely ever see them listed in a price guide, other than the Maris proof of 1967, which is listed in the SCD for big bucks ($1,275. in NM in the 2005 SCD). Why do they list ONLY that one? Can anyone shed a little more light on these mysterious cards, and whether they're really worth trying to obtain?