Missing factions? (Please no spoilers)

Hey guys, I'm just a little bit into the campaign now (escaping Howloon level?) and I've been wondering about the faction teams in multiplayer and maybe why some factions aren't included. I'm assuming its because the factions aren't included in the campaign itself.

So in the multiplayer, I've seen these factions:
-Black Ops
-Op 40
-Spetsnaz
-NVA (North Vietnamese Army)
-Trepos... ? (Cuban forces, I don't quite remember they're name... something around those lines)
-SOG

These are the forces I thought would be appropriate to put into the game:
-SVA (South Vietnamese Army) --Since the SOG only consisted of the United States Special Forces, Navy SEALs, Air Force, CIA, and Marines, I'm wondering where the forces from actual South Vietnam might be.
-French Militias..? --Maybe the French appear in the campaign for the beginning of the war in Vietnam since they had colonized the whole nation before Soviet advance...
-Viet Cong? --No Viet Cong troops? What I'm thinking here is that they couldn't have multiplayer faction for them because there were so few, and thus real "Battles" didn't quite ensue. I'm seen bits that they appear in the campaign... (Xbox LIVE achievement requires you to silently kill __ number of VC troops...)

Once again, the multiplayer factions all have to do with the storyline of the game itself, so even though these factions took part in the Vietnam War (or on a greater scale, the time period of the Cold War before, during, and after the Vietnam War) they might have not taken part in the game. So far I am loving this game--multiplayer is more balanced and fun than ever, and campaign/storyline is interesting and gripping so far... I would like to see bonus campaigns/maps/something that bring focus around a lot of other parts of the Cold War, maybe even Korea. I don't know, just an idea. What do you guys think? Thanks for the input.

Yeah, Tropas** the name of the Cuban forces.