Are pre-order bonuses made after a game is finished?

I want to know if the content in pre-order bonuses would exist without pre-orders. In other words, if Gamestop has pre-order content is that content created just for them or is it just content that was ripped from the complete game and sold back to the consumer as a "bonus"? I recently bought Mortal Kombat 9 and got the pre-order Scorpion costume, however there were other bonuses like Sub-zero's costume (Best Buy) and Reptile's (Amazon). These costumes are in the game though because you fight against these guys with these costumes in certain parts of the game but you can't use them yourself unless you have a code. And they recently announced a DLC for all the pre-order costumes. So I was wondering if there were no pre-order bonuses for this game would these costumes exist? This question also applies to other games with pre-order bonuses. Thanks!Are pre-order bonuses made after a game is finished?
Probably

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