James you're not thinking this through. His employer is in his home country, paying into a bank account in that country. The only time his pay is exposed to the Thai banking system is when he makes an ATM withdrawal
Emergency travel documents are usually only valid for returning to your country of origin and any transits required to do this. The ones that I have seen have explicitly stated this.
I don't know about Chonburi not accepting documents from the US embassy, they should as that's one of the available options to show sufficient funds.
The affidavit itself is notarized. So in effect they are verifying that YOU are who you say you are. Much like any notary, they are not certifying that the document is true but rather certifying that your are who you say you are. I don't think the Thais know the difference between something being notarized and something being certified; the US Embassy won't certify anything, it's not a service that's offered. What that means is you could write an affidavit stating your income is 5m thb per month, and as long as your identity documents are in order they will notarize it.
Don't think that applies to or man Harris, but good to know! Was a real huge issue back in the early 2000s for my mother who worked in both Saudi and Israel. She has about 40 booklets because each trip she had to get a new passport...
It's also my experience in the more distant past that passports are invalidated upon applying for a new one unless an exemption is given.
Not my direct experience, but my mom was disallowed from holding two valid US passports at the same time and she had valid reasons to do so. At the time she was married to a high level us government official based overseas and also had very legitimate uses for both passports.
I don't think it's common. Maybe I've just had several exceptional experiences thorough my lifetime...