"At this point, since we now have all of the possible references contradicting themselves, this neutral researcher says "to hell with it" and closes the subject."
So if you were to say... grow up differently... under different circumstances... it would be all right. HA! Take that obsessive fanbase!
Thanagar's champion, Hawkman can talk to birds. He also can't talk to birds. Sometimes, he can't even speak normally at all! Even if he could talk normally, or to birds, there are no birds on Thanagar, because it does not exist. Hawkman was sent here to study Earthly police methods, because Thanagar's own methods suck! That's OK though, because Thanagar still does not exist! Yet it is populated by peaceful barbarians! Who are stupid, and also warlike!
Like all non-existant Thanagarians, Hawkman has human legs! Which are reincarnated legs! Alien legs! Egyptian legs! Thanagarian legs! Bird legs! God legs! Bird-God legs! This is because he's... a God! An Earthman! A Thanagarian! An American! An Egyptian! A common human! A reincarnated prince! A hawk! A God! A God-Hawk! A Hawk-God! A God-like Hawk God of Other, Less Godly Hawks!
This whole mess doesn't remotely fit... MOVING ON!
So rather than rebooting the Legion and derailing its momentum, the solution was to base the team on a pocket universe that was created by the Time Trapper that did have a Superboy, Supergirl, Krypto, and so on. In essence, there was a small piece of the Silver Age that made it through Crisis, but only in regards to one specific group.
Surely that wouldn't create any problems.
Wolverine: No, no, don't change the subject here. Why aren't you dead?
Magneto: Oh, that. Well, you see, that wasn't me.
Wolverine: Oh really now?
Magneto: It was actually Xorn's twin brother, possessed by the sentient mold Sublime, pretending to be me, pretending to be Xorn.
Beast: That defies all logic!
— X-Men: Death Becomes Them (note that this is an entirely accurate description of the canon at the time after all the retcons.)