I'm wondering whether you only get this bonus if you buy/pre-order via Steam, or whether it's all the same if you buy from other places since you still get a Steam activation code at the end of the day. Pre-ordering/buying has become kinda complicated these days, especially in cases like these where I don't know whether a seller simply hasn't updated their description or their version won't contain this bonus.

I guess it's unlikely that someone official is gonna read this, but does anyone here have had experiences like this in the past? Not the first time Valve has done this sort of crossover promotion after all.

All answers are appreciated!