For those saying a visa can be transferred they are getting confused with their extension stamps (or even initial visa issued in country). These are stamps issued by immigration in Thailand.
It is not possible to transfer a visa sticker, or change the PDF file sent to you via the evisa system.
What can they transfer? They cant transfer a sticker. They can’t update the PDF evisa that was sent if you via the evisa system.
They can and will transfer extention of stat stamps issued in Thailand and indeed visas issued in Thailand but cant transfer visas issued abroad from the MFA.
Their agent isn’t wrong. A DTV visa is issued by the ministry of foreign affairs and is either a sticker in your passport or a PDF file. Neither can be transferred to a new passport.
You carry both passports for validity of your visa.
Yes LTR holders report once a year. I’m pretty certain OX holders do so too - although I can’t be 100% certain on that. There’s so few of those around.