Missing Geocodes

The list of geocodes contains several obsolete geocodes, most of them are the codes of the districts (and their constituent subdistricts) of the provinces Sa Kaeo, Amnat Charoen and Nongbua Lamphu before these were created. For the subdistricts almost all the obsolete codes are those for minor districts created after the original geocode table was created. But there are a few cases where a geocode is missing for other reasons. I already could find the right answer for two cases - in Khura Buri and Thung Si Udom one of the subdistricts was reassigned to a different district, for Khura Buri the historical center of the district, for Thung Si Udom the subdistrict was included when the minor district was created, but one year later this was reverted.

The other cases where geocodes are missing are not so clear:

• In Pa Bon the missing number should belong to a subdistrict created between 1987 and 1991, and the population numbers at DOPA list this subdistrict (without a name) for the 1993 statistics. But no trace in the Royal Gazette for a subdistrict creation or abolishment
• In Mueang Nakhon Si Thammarat two subdistricts are missing, which seem to be named Sala Mi Chai (ศาลามีชัย) and Na (นา). But still haven't found the year they were abolished, and to which subdistrict they are added.
• Other ones I haven't investigated in detail yet are in Mae Sai, Phon, Mae Sariang, Phu Luang, Kaeng Khoi and Pa Daet, each have a single number missing. I don't recall to had any unknown subdistrict in the populations numbers till 1993, so if these numbers belong to an abolished subdistrict this must have happened before 1993.