I'm not entirely clear on whether you are asking about the Free Space page for Vinh Long and Soc Trang or if your question pertains to categorization.
If your question is about the Free Space page for Soc Trang and Vinh Long, then the reason Dustoff isn't listed because I haven't gotten around to getting it added yet as being present at Soc Trang. There are still important aspects from both locations missing that I just haven't had time to get to yet. It's a work in progress, but my goal is to make sure no one gets left out who served or was killed while serving at either of these two locations.
The only Dustoff (Air Ambulance) unit I've run across at Soc Trang so far is the 571st Medical Detachment. They would have arrived at Soc Trang in early1968 after training at Nha Trang in1967. They appear to have only been at Soc Trang for a short time before being reassigned. Does this sound like the Dustoff Unit who was there when you were, or should I be looking for an additional/different Unit?