Map Validity

I found this map of Vietnam and was wondering if it's legit. 

http://www.globalsecurity.org/military/world/vietnam/images/dai-viet-map-le.gif

The reason I ask is because of the discrepancy of information from my reading materials and the map.  Note the region of Cambodia labeled as annexed in 1818.  According to many sources I looked at, Cambodia was a satellite Kingdom or protectorate of Vietnam prior to 1835.  Emperor Minh Mang annexed the region in 1835 and that area formally became part of Dai Nam(Vietnamese empire).  Vietnamese direct rule of Cambodia lasted about five years, 1835-1841.  After 1841, that area was relinquished from direct Vietnamese rule.  Cambodia won back its semi-independent state before its annexation by Vietnam.  So, why is it labeled as Vietnamese territory all the way from 1818 up to 1863, when Cambodia became a French protectorate?

Timeline:
Cambodia was a Vietnamese protectorate (1813-1834) under Vietnamese influence--> Cambodia became directly ruled Vietnamese colony (1835-1841) --> Siamese Vietnamese warfare on  Cambodian soil (1841-1847)-->Direct Vietnamese rule of Cambodia ends and Cambodia comes under influence of her larger neighbors as a joint Vietnamese-Siamese protectorate (1847-1863)--> Cambodia is annexed and directly ruled as a French protectorate (1863)


Edited by VinaCapital - 05-Jan-2011 at 01:44