Comic Book Questions Answered – where I answer whatever questions you folks might have about comic books (feel free to e-mail questions to me at email@example.com).
My pal Alan C. asked me on Facebook:
I forget but how did Supergirl gain entry into the Legion? Didn't they have 'no duplicate power set' rule? Mon-El got over this by not being affected by kryptonite, so his powers weren't 'exactly' the same as Superboy's and Ultra Boy's 'penetra-vision' can see thru lead. I know they explained it but I've forgotten. May have to turn in my flight ring.
The real reason, Alan, is that the rule was invented WAY late into the game, after the Legion had already admitted a bunch of characters with powers similar to Superboy, like Supergirl, Ultra Boy, Mon-El and Star Boy (back when Star Boy had powers like Superboy).
The "Powers must be unique" rule was not introduced until "Superboy" #195 (by Cary Bates and Dave Cockrum) as a reason for why a new prospective member, Erg-1, could not join...
Obviously, being made out of pure energy, Erg later showed his unique power at the end, when he seemingly explodes. But don't worry, he returns and becomes a member of the team and gets the name Wildfire.
So yeah, because the rule was introduced 15 years into the Legion's existence, it naturally conflicted with the past (by the way, people are CONVINCED that it happened earlier in the Legion's history, but it did not. I even did a Comic Book Legends Revealed on the topic years ago). That said, now that they DID have the rule in place, that led to them doing exactly what Alan described, coming up with reasons why Ultra-Boy's powers were distinct or Mon-El's. But what about Superboy and Supergirl?
Well, that exact topic was addressed in "Superboy" #212 (by Jim Shooter and Mike Grell) and...well, be prepared for an unsatisfying explanation!
It's the basic equivalent of "You want to know why? Because shut up!"
So yes, it really is as simple as "Superboy and Supergirl are exceptions." I mean, Superboy DID inspire the club to form in the first place, so I could see why they would make an exception for him and his cousin, but it's still pretty funny.
Thanks for the question, Alan! If anyone ELSE has a comic book question that they'd like to see answered, drop me a line at firstname.lastname@example.org!