回複：I put them in one big envelop with two separate folders

I know sometimes we do want to save some money, but American is American, you can say they are stupid, but that is how they do the work. I will say you are lucky because it worked for your case, but you will waste lots of time if they mess up your documents and even you can say nothing because it is YOUR fault. 

I will suggest that you treat as separate cases. To be safe.

YMYD