No need to waste a 3rd bag IMO. Even though the bones may not seem pronounced they are still sharp and it only takes a pinhole to lose the vacuum. Plus any handling of the bag increases the likelihood of puncture. The meat has already lost the adhesive moisture and transferring it a 3rd time makes little adhesion even more of an issue. Why not place a piece of tape on the bag over the bone area as cheap insurance against pin holes? If you have 80% adhesion you will be fine – a perfect vacuum is not necessary! Air in particular on the bone side and ends is no big issue.