The idea is that those twelve hours are experience that you have, logged on a representative type. It doesn't matter one bit whether that experience was on a G-reg or N-reg as long as it's on a type that fits your UK licence/rating. In the end it's up to the person signing your licence, is he/she happy to accept those hours and extend the validity of your rating? I know I would happily accept it, but I'm no examiner.