Ah but the young and old Kazrans did not have 100% the same atoms. They had different clothes. Had they hugged nude, the BLE would have been more likely to kick in. However, that would've been right weird and the censors wouldn't allow it. Also, tje Doctor was absolutely planning on the two Kazrans meeting, so even though it wasn't mentioned that he did, he may have placed some sort of field around the younger Kazran just in case of . There! Hole filled!