Non-Steam version and DLC

[Fred DM]

so, like Assault Squad, MoW: Vietnam is available as either a Steam version or a non-Steam one (for example from GamersGate or GetGames). and like Assault Squad, Vietnam has DLC available (currently only the SE upgrade) exclusively on Steam.

from what i've read, Assault Squad could be activated on Steam regardless of where it had been bought (i wouldn't know as i've purchased it on Steam anyway).

my question is how it will work with Vietnam. how do people who bought the standard edition outside of Steam upgrade to the Special Edition? can Vietnam also be activated on Steam?

Edit: word from GetGames is that their keys cannot be activated on Steam. so how exactly are owners of non-Steam standard editions supposed to upgrade or purchase any upcoming DLC that might be released?