@Re**
, in theory, IF you're on an extension when you get your new passport you are supposed to go transfer the stamps to the new one.
You probably would be able to show both, have the passport control people move your stamps and stamp you out on the new one at the Nong Khai border.
@Amor****
, they're on a on a visa exempt with a 30 day extension, can they just show both passports at Nong Khai when they exit the country?