Do you need proof of leaving Thailand between flights when applying for a METV?

I applied for My METV online through Washington DC. Only need proof of entry and final flight home, which I have since changed.

I brought my Vietnamese girlfriend to join me in Chiang Mai for six months using the METV. The immigration officer in the Thai embassy in HCMC was only interested in my booking return flights at the end of the six month period. They weren't interested in showing evidence of border runs in between. In fact, I used the online service to book her first 30 day extension and then I've booked flights for us to visit Laos as a border run before returning in late October. Immigration weren't interested in any of that, just the arrival and departure flights after six months.

As a rule you show your entry flight to Thailand and then a flight leaving in 60 to 90 days and then a flight returning, to prove to the Embassy the reason you need a multi entry tourist visa. Submit what you have and if they need more flight bookings or information they'll email you