Again, why?
Why are people not able to accept that Lex Luthor gave these four metahumans codenames during his research?
He may have been able to find out Diana Prince's or Barry Allen's name -- he definitely knew Victor Stone's name. But there's no way he knew Arthur Curry's name. So, why is it not plausible that Lex Luthor wouldn't be like, "This guy lives in water and swims with almost a sonic-boom speeds ... Aquaman. That's a good code name for this file."
"This girl is mysterious and there are the rumors and stories of her from World War I. Her powers are wondrous. Code name: Wonder Woman."
"This guy is literally turned into a Cyborg."
"Wow. That guy just broke up the robbery in a flash!"
This is an organic way, actually, to give them all their Justice League codenames and have Bruce refer to them by that since those files are now his files.