If the SCMP article and this article are to be believed, sounds like yes, entering the country and then going back to the airport to check in is the only way. I think what’s not permitted is the return to the airport you came from while in transit. I guess I’ll find out in early March when I have a same day turn (fortunately 8 hours between flights, so time enough to head into HCMC and then back to airport). If I get stuck, well...that’ll be an adventure.