Have Us Passport and obtained METV from Washington in 2018, then obtained a 30 day extension is CM in 2018, then an SETV from Vientaine in 2019, then departed back to US. Now heading back in August this year. Can onward travel for either an US obtained SETV (or in country exemption stamp) be a booked bus ticket (assuming I can somehow get a copy of that stateside) from Udon Thani to Vientiane?