The encyclopedia page for vietnam appear to say that collar insignias ceased to be used in 2008 at which point the army switched to shoulder ones.
On this picture taken in 2014 however, you can clearly see that collar insignias are worn.
http://www.gettyimages.com.au/detail/news-photo/lieutenant-colonel-mac-duc-trong-and-lieutenant-colonel-news-photo/493969939
Any know if this is a case of collar insignias being worn on operational gears with the shoulder ones being reserved for other type of dress ?