New Rachel has tried to make sense of the Legion of Super-Heroes’ existence within Supergirl continuity and wrote us an email, outlining her theory on how they fit in with the Legion Ring we were shown in Season 1.
Although the Legion of Super-Heroes was only formally introduced into the Arrowverse in this season of Supergirl, the idea that they existed in that universe was established all the way back in February of 2016, where on both season 2 of The Flash (in the portal to Earth 2 that contained glimpses of alternate universes and timelines) and season 1 of Supergirl, Legion rings were shown to exist. The Supergirl example, as it was depicted in the Fortress of Solitude that Kara visited, is the more prominent of the two, and will be the one focused on in this theory.
The Supergirl universe’s version of the Fortress of Solitude is explicitly depicted as being Clark’s, and as an audience we assume that all of the belongings there are his as well. So, of course, this Legion ring belongs to him, and given that there’s canonical precedent for Clark being trained by the Legion prior to becoming Superman, or his training leads him to taking up the mantle of Superman, one can say that such is also true on this Earth.
However, the Legion shown in this season, assuming they’re the same Legion he met, has different rings:
Thus, it is questionable that they trained him. Especially so given how new they are in heroism, having only been around for 7 years at this point, in comparison to Clark’s 12+ years of having been Superman.
Another point, in this, is if Superman has already met + been trained by the Legion, including Mon-El, then why did he not recognize him in 2×22? The answer may, of course, be that his memory was erased to protect the timeline, but then what was the purpose of the training in that case and why would they have let him keep the ring?
The answer that, at this point, makes the most sense, is that Mon-El was not the founder of the Legion that Clark met, and that Mon-El, in true Legends of Tomorrow–esque fashion, changed the future when he was sent into it via a disruption/wormhole in 2×22, essentially making himself an anachronism and aberration in the 31st century.
The rings are different because they belong to two completely different versions of the Legion, in two separate timelines.
Timeline 1: containing Legion A (using the rings shown in 1×15) was stable from before the series began all the way until 2×22. This Legion was the one that trained Superman, and lasted longer, being established before he arrived and thanks to, most likely, the influence of him and Kara, without either of them having to travel to the future themselves to found it.
Timeline 2: containing Legion B (using the rings shown in 3×10) diverged at 2×22, and is the one we see on-screen currently (or saw, on-screen, as of 3×18). This one has only lasted seven years thus far, was solely founded by Mon-El, and solely inspired by Kara and her work as Supergirl.
Now, will this ever be addressed in-canon? Most likely not, as it isn’t relevant to the storyline and nobody besides Superman himself would notice the change. But, I thought it might give some people peace of mind regarding the divergence of this version of the Legion from the traditional one, as well as solve an inconsistency with props that were each given literally two seconds of screentime.
Stay super,New Rachel