ouch, looks like I have a problem after all. It seems logical that if the slaughter tag -although having only a six digit flock number on the outside, contains a longer electronic number then two yellow tags on the same sheep will give two different numbers on one sheep leading to confusion when being slaughtered, the quick answer would be to remove one of the tags. I think I need to check with the manufacturers if they do add extra electronic numbers on slaughter tags. on the face of it I'm not sure they would have extra numbers on slaughter tags as they would not be know to anyone, the breeder, any subsequent owner (me) or anyone I sell on to. Thanks everyone for trying to help me, I really appreciate it.