Help, no original Thai birth certificate. What now?

I am not 100% aware of Dutch legislation in this matter, although it seems to me that the official is not really aware of the values ​​of an official duplicate of the birth certificate issued in Thailand.
You could also write to your ministry about this….
Option 2 – on your next holiday in Thailand you can get married in Thailand and have your marriage legalised in the Netherlands afterwards.
Avoiding the paperwork won't work, but finding the solution certainly will.

Dear Michal,

I have also had this problem in connection with the RNI and presented this problem to them.

Response from the RNI:

— The birth was registered before 1995
For a person born in Thailand, a birth certificate is issued only once. This original source document must be retained by the holder at all times. The system of extracts from the birth register is not common in Thailand and, if it is, a laborious affair.

The source document is translated into English in Thailand, after which a copy of the source document in question is sealed to the original translation. The translation with attached copy must be presented together with the original source document to the Legalization Office of the Thai Ministry of Foreign Affairs in Bangkok. Without the original source document, no legalization stamp will be issued by the said Ministry. No legalization will be placed on the original.
Although the text on the legalization stamp states 'seen at the Ministry of Foreign Affairs', this is in fact a legalization.

No more birth certificate?
The Dutch embassy in Bangkok informs that the Thai authorities can issue statements stating that a particular birth certificate does not appear in their registers (for example due to fire).
If a person no longer has access to his original birth certificate and a new copy cannot be obtained from the town hall ('Amphur'), ​​the town hall can be requested to have a replacement declaration (in the form of a letter - Letter of Birthplace Certification) drawn up regarding the birth. This must be done in person. Witnesses are also required for this and (if possible) documents relating to the birth must be submitted. This is therefore not a birth certificate; at most comparable to a certificate of birth awareness. The date of birth is stated in the travel document and the home registration form. In that case, the 'declaration Thai authority + home registration form' can be stated as the source document for processing in the BRP. The “Letter of Birthplace Certification” is a document as referred to in article 2.8 paragraph 2 under d BRP. Incidentally, it sometimes happens that the date of birth is not stated in such a declaration.

— The birth was registered in or after 1995
In 1995, the Thai authorities adopted a computerised system of registration of public deeds. A certified copy can be requested by the person concerned or any other interested party at the Amphur or District Office where the registration of the legal act took place.
Obtaining an extract from the birth register is even easier. The person concerned or another interested party can submit an application (or have it submitted) at any 'District Office' in Bangkok or at any city hall ('Amphur') in any province. The person concerned must present the ID card with this application. An extract is issued and signed by the competent authority. This signature confirms that the information in the extract comes from the 'Registration Database' of the 'Central Registration Office', 'Department of Local Administration', Ministry of the Interior.