What's the difference between the 5 Samsung Vibrant models?

I have a T-Mobile Galaxy S Vibrant, which has the Samsung model number SGH-T959. However, Samsung's [download page](http://www.samsung.com/us/support/downloads/SGH-T959ZKATMB) has 5 different sub-models: SGH-T959ZKATMB (appears to be the "default"), SGH-T959ZKDTMB, SGH-T959ZKMTMB, SGH-T959ZKBTMB, and SGH-T959ZKBTMK. The only difference in the downloads is that the ZKBTMK doesn't have any manuals or instructions. Apart from that, all the files are dated the same across all 5 versions. What are the differences between these phones? And how can I tell which one my device is?