I've seen miscut cards before, but the extra border (and there was a LOT of it) was always black, so I assumed that the sheets were printed with the cardface set on a black background, not just black borders around the cards.
In which case, I would say that the white borders is probably a lie.
On the other hand, I wouldn't be surprised if, at some point, Decipher switched to black borders on white backgrounds to reduce printing costs... Didn't D switch printers at some point? That could have something to do with it. The miscuts I remember seeing were all in the movie blocks.