Congratulations on 12 years! To my understanding, wound healing can be more difficult or delayed.in a radiated area due to reduced blood flow, reduced oxygen, necrosis and fibrosis. Other factors may compound matters like poor diet, lack of protein, smoking, alcohol, diabetes, and other lowered immune system disorders. Some need to see a wound care specialist, and may need HBOT, Hyberbaric Oxygen Therapy. I had 30 HBO for a tooth infection that was not healing properly, 20 before, and 10 post extraction. Post neck dissection, stitches are left in longer for healing, if you had prior radiation.
Good luck with everything, and hope the tongue finally heals properly.