This actually came up over at the 2K forums and one of the users there had a pretty good hypothesis on what you're seeing with the extra attire slot. I'll quote him:
"This is just a feature that I mentioned would be nice... it's not a limitation on creating alt attires...
When you create a caw... there are 2 attire slots. If you were editing a wrestler, you still had the 2 attire slots and could use them... but... if you set the edit as an alternate attire, only the first attire slot could be used... now they've fixed it.
Would like to see us be able to create more than 2 alt attires for caws and have them recognized like edit a superstar is... but... I'm sure that's a bit more complicated."
I'm still a little confused by this. What benefit does it serve for the regular non-caw roster?
Thunderlips (responding to my question):
Okay... let's say you were to make a plain old created wrestler. There is an attire 1 and an attire 2. You can select either of these attires when playing matches.
However, now you want to make an alt attire. Let's say it's AJ... You create an AJ with a red attire scheme on attire 1... then you select attire 2 and make a white attire scheme... then you go into the info, save it as an alternate attire for AJ... when you go into exhibition, you can only select attire 1... now you have access to attire 1 and 2... it actually doubles how many alternates you can have.
Yeh I just read this too and it seemed to make sense until I read a comment from another user which changed my mind again because we could always make 2 attires per caw slot but if you saved it as an alt attire for the superstar it would only use the attire in the slot 1(which I think it called 'original attire').
So I'm thinking it will still do that and nothing has changed in regards to how many attires we are allowed per superstar and all we are seeing in the pictures that are confusing people is a change in layout, as the extra attire slots are shown next to the superstar (in 2k16 they were listed before that screen when you clicked 'edit' on the superstar) So when you choose to save it as an alt attire it'll still use the attire in slot 1.......that's my theory anyway. Lol