the difference is that she has a back! I spent a while looking for the difference too :3 but in the far right one you can see that the suit looks like it's a one piece? or a straight cut high-low shirt XD
You're not the only one! I kept looking and looking and I'm like....did we forget the third one and do a duplicate. Woops. Given that this is in black and white, the team may be planning to do different colors later. Not sure, but that might be why.
Nice concepts (both these ones and the two ya posted before), though I'd prefer to see Kory in something more akin to her classic one piece costume, or her skirt and top uniform from the cartoon (the first one, not the chibi version XD). Not trying to be lewd here or anything, just naming some of her better outfits before the New 52 screwed things up XD...Kory's a balancing act of sorts, she shouldn't be covered up like a nun given her alien culture and free spirit personality (she's the opposite of the reserved Raven after all), but whatever she's wearing shouldn't look like its held on by glue either lol.
Hope that makes sense and helps with later drafts.