That's what I meant. I do not have a letter from HMPO but I didn't have 10 years ago either and the details were transferred.
Surely everyone who obtained an extension on a passport which is valid for less than 12 months has an extension which expires on the same date as their passport?
I renewed my passport in September last year. I haven't yet told Thailand Immigration.
As
@gotlost has stated, my old passport and extension are valid until midnight 06:06:2020.
The majority of people renew their passports during the currency of their existing extension- as, indeed, you did. You just didn’t bother to have the Immigration stamps transferred to the new passport. Not sure if you will have an issue with that
According to the American embassy website it is Thai Immigration “law” that requires you to transfer the stamps to the new passport:-
“Thai immigration law requires entry/exit stamps and Thai visas be transferred into new passports. After receiving your new passport, please visit any Thai immigration office to have the visa transferred. The letter to facilitate visa transfers comes standard with all passport renewals and is provided without fee.”
From Richard Barrow’s blog...
Once I had my new passport in hand, I next headed to Immigration to have my valid stamps transferred over. You don’t need to rush there as I did, but I wanted to finish everything within one day. The procedure here is very simple. You will need to photocopy and sign the photo page of both passports. Then photocopy every page in the old passport that has a stamp. These photocopies need to be signed too. You also need to fill out a form with details about your old and new passports. Then, present all of this and the letter that you got from the British embassy to the Immigration officer. I was finished within about 15 minutes. The best thing of all, it was free to transfer the stamps.
The only thing I need to do now is to register my new passport at my local bank. If you didn’t know already, when you get a new passport, you get a new passport number. So, basically, any place that you used your passport to register for something, you need to go back and tell them. Again, there isn’t a rush and in fact, I didn’t do it for a few years last time. It is only a problem when you need to do something and your passport numbers don’t match. You will then need to take your old and new passports with you.