With last week's announcement that HBO Max will complete and release the "Snyder Cut" of Justice League -- Zack Snyder's extra-long director's cut, which will flesh out backstories and include at least one new character not pictured in the theatrical version -- some fans have wondered which version will "count" as it pertains to the continuity of the movies. At present, there is no reason to assume the Snyder Cut will overtake the theatrical version as the accepted canon going forward, since it is essentially the same kind of extended director's cut that lots of movies get on DVD and Blu-ray. If it does, though, Zack Snyder and DC could have been gifted an easy explanation.
First: Justice League has had relatively little direct impact on the movies that have followed it. Both Aquaman and Shazam! referenced the events of the film, but neither went into any kind of depth at all. Anything with the same basic plot as the version released theatrically would not shake the brief, almost dismissive references made in the other films.
If, for whatever reason, somebody decided that they wanted Zack Snyder's Justice League to be the definitive version of the film, though, The CW's reality-hopping "Crisis on Infinite Earths" gives them the perfect opportunity.
During the TV crossover, which brought the Arrowverse characters into contact with heroes from Titans, Stargirl, Smallville, the 1989 Batman movie, and more, Ezra Miller's Barry Allen arrived, meeting up with Grant Gustin's version and having a brief conversation in which, among other things, the Earth-1 version of Barry gave him the idea for the name of "The Flash" -- something he never actually used in Justice League.
In the moths since "Crisis on Infinite Earths" aired, fans have wondered whether there might be some passing reference to the events of the Crisis in Miller's next screen appearance, which at the time was expected to be The Flash. Instead, he will be one of the characters whose backstory will get a tweak in Zack Snyder's Justice League, and that makes us wonder: what if the events of the Crisis could explain the minor change in the continuity of DC's film universe?
At the end of the Crisis, the worlds of The CW's DC multiverse were realigned, with the major ones consolidated into a single "Earth Prime" where the shows now take place. The final episode of the storyline revealed that a version of the multiverse still exists, but with some minor changes, and that it is shut off to the Arrowverse heroes.
That would not mean that the CW shows would have any kind of major impact on the DC film strategy, or that you would have had to watch "Crisis" to understand it. Instead, it would just be a fun, clever, throwaway reference that would give them an easy "out" for any changes Snyder's version of Justice League might introduce while rewarding the same kind of hardcore fans who made #ReleaseTheSnyderCut a thing to begin with.
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