The actual decrees were the following
- Revolutionary decree 24, December 21 1971 - merge of the provinces Phra Nakhon and Thonburi to the province Nakhon Krung Thep Thonburi (นครหลวงกรุงเทพธนบุรี). This includes the merger of the Provincial Administrative Organizations to one new one named องค์การบริหารนครหลวงกรุงเทพธนบุรี.
- Revolutionary decree 25, December 21 1971 - merge of the municipalities Krung Thep and Thonburi to the city Luang (เทศบาลนครหลวง).
- Revolutionary decree 335, December 13 1972 - establishing of the Bangkok Metropolitan Administration (เทศบาลนครหลวง). This includes many smaller changes, like the abolishing of the muncipality, the PAO and the 11 sanitary district; also the district were renamed from Amphoe to Khet, and all of the new posts were defined.
It was BKK Photographer who made me notice the celebrations on this anniversary, which however seem to be rather quiet, with some booths set up on the plaza in front the administration building next to the Giant Swing. For some photos see his set of flickr.