Those AI era Sixer uniforms have been in 2K since the inception of 2K. They were just tacked on as retros the year Philly switched back to the old school logo, kind of how Washington's jerseys from last year are now retroed.
Also, I'm not trying to pile on, but are you referring to the list brought about by a random poster saying he had a friend who worked for 2K. I'd love for additional historic teams in 2K12, but I wouldn't use that post on that website as a basis for excitement. It was so strange how everyone assumed his word to be true.