While both Khwaeng and Tambon are the third level territorial subdivision, the difference between the two is at first that Tambon are subordinate of the Ministry of the Interior, while the Khwaeng are under the Bangkok Metropolitan Administration (BMA). I still have to find the details on how the Khwaeng are actually administrated, the Wikipedia article on this is still very incomplete and needs expansion.
Anyway, there have been two announcements on the creation of new subdistricts after 1997, both issued on December 1 2003.
- In Chatuchak district (เขตจตุจักร) four subdistrict got created - before this change the district consisted of the single subdistrict Lat Yao (แขวงลาดยาว). The corresponding announcement was in Royal Gazette volume 120, issue พิเศษ 138 ง, pages 28 to 34.
- In Thonburi district (เขตธนบุรี) the two new subdistrict Samre (แขวงสำเหร่) and Dao Khanong (แขวงดาวคะนอง) got created, increasing the number of subdistricts from 5 to 7. The corresponding announcement was in Royal Gazette volume 120, issue พิเศษ 138 ง, pages 35 to 42.