i think immigration officers should check in different side of computer if want to see history for old passport.But if doesnt check they dont see very old years.
there was a police man(cambodian) 10 years ago in front of Phnom Penh embassy he was making thai tourist visa.I didnt accept him.Then he was angry to me haha.Is he still there?That time visa was easy to get.Now very difficult.If someone sees him please tell me i want to contact to him.Maybe retired haha
Dont change passport inside Thailand.Still will be same stamp.Change in other country Laos Or Cambodia.Or apply in Bangkok and try to enter to Thailand from NongKhai with current passport.And wait your passport comes to Thailand.Then everything will be allright.