I've got a guessing game here too. I planted apple trees from Morrisons a couple of years ago and two of them died back, then sprouted very healthy branches from below the root stock. No fruit this year but I'll be interested to see what happens next year. If no fruit appears again then they will be pulled out and new ones planted. I think I was told that the bushes were probably rooted onto an old variety of apple, so if I get fruit it would be very interesting to try to find out what they are.