We flew in April. No form needed. Had to check out at INM desk and have Passport stamping us out. When we went to check in the guy at the beginning of the que looked at our passport to see our stamp that date and we were able to go to check in. If you don’t have checked luggage I guess they will check your passport for stamp at the boarding gate. When coming back into Mx when going to the passport immigration guy he will stamp your passport back in to Mx. INM is last place you leave Mx.