I am 99% sure the Ace SOCOM is NOT available in 2 lengths. I have never seen in person or a picture of an "extended length" SOCOM nor have I ever been able to find one on any website (including Ace's) any information about it. The only options I know of are 1) Coyote Brown instead of black and 2) fixed position with extended foam pad.
Treetop, you're probably thinking of the Ace Skeleton versus the Entry stock. Those two are nearly identical but the Entry is a bit shorter.
As for the 11" to 13" listed at the bottom, I think that's just a typo. All the other stocks on the page list a LOP and an overall lenght. I don't feel like taking mine off right now, but this is how I see it:
Fully Collapsed: LOP = 7.5", Overall Length 11"
Fully Extended: LOP = 9.5", Overall Length 13"
Since you bought this gun used, I wonder if the previous owner didn't somehow modify it to be longer. Maybe you're right and you do have some very early prototype in which case, hold onto it, you never know, it might be worth something.