I ordered a Schwalbe Marathon Supreme tire for my KH29. Today I received it but it is a 28X2. I went back to check the receipt and it does say 29X2. The 28 won’t fit will it? Is this the way the sizing works or is it wrong? I don’t want to attempt to put it on until I know. Thanks.
Both of the tires have a bead seat diameter of 622, and will fit your rim. 28" or 29" is highly relative, and has more to do with the width of the tire than the diameter. Traditionally 50mm and under would be named a 28" tire, while over 50mm would be considered a 29". In truth they are both made to fit the same rim.
According to Sheldon Brown 28x , 29x, and 700c designations can be used interchangeably.
Edit: Yeah, what Jerry said. 
Thanks. I was hoping it was something like that.