@Ju***
When I got my new Passport, the embassy gave me back my old, devaluated Passport (apart from those pages who still had a valid visa in it, like my Thai Non-b and my USA) and some letter I did not specifically asked for.
On my next Visa visa run a few weeks later, I gave Immigration in Sadao both my Passports and that letter. The officer passed my documents to a girl in the next boot who put a transfer stamp on the first page of it
Only problem I had, after the girl stamped my passport I was of to Malaysia only to be sent back as she didn't stamp me out of the country.