The 2018 Arrowverse crossover, "Elseworlds", was almost named after a completely different DC Comics story, Identity Crisis. Written by Brad Meltzer, Identity Crisis was a 2004 limited series that starred the Justice League.
The three-night event ended with Tuesday's episode of Supergirl. The crossover, which also consisted of The Flash and Arrow, saw Arkham Asylum doctor John Deegan (Jeremy Davies) rewrite reality with the help of The Monitor (LaMonica Garrett), causing Barry (Grant Gustin) and Oliver (Stephen Amell) to swap lives. To set things right, Barry and Oliver enlisted the help of Supergirl (Melissa Benoist) and Superman (Tyler Hoechlin). "Elseworlds" also featured the Arrowverse debuts for Ruby Rose as Batwoman and Elizabeth Tulloch as Lois Lane.
In a clip from the "Inside the Crossover: Elseworlds" bonus feature released by EW, Arrow consulting producer Marc Guggenheim revealed that another name was considered for the crossover. It was almost called "Identity Crisis", which would have been an homage to another DC Comics story, but Guggenheim admits that giving it that name would have been "false advertising." He said:
The problem is that ‘Identity Crisis’ is another different iconic DC story. While the title would work perfectly for this, it would really be false advertising, because we’re obviously not doing the Brad Meltzer, Rags Morales Identity Crisis story.
It's true that calling it "Identity Crisis" would have painted a very different picture of the crossover for DC Comics fans, even though the name would have perfectly described what happens to Barry and Oliver. However, Identity Crisis doesn't feature superheroes swapping bodies or identities. Identity Crisis is a well-known story where members of the Justice League are shaken by the murder of the Elongated Man's wife, Sue Dibny. While working together to get to the bottom of the mystery, they uncover shocking secrets that their teammates had left buried for years. As Guggenheim points out, the plot of Identity Crisis really has nothing in common with anything that happened in "Elseworlds".
The crossover's actual namesake, on the other hand, is at least relevant to the main storyline in the event. In the comics, Elseworlds is a series of "what if" stories that focuses on alternate scenarios starring DC characters. What Deegan does to Oliver and Barry is basically create an alternate scenario that imagines Oliver Queen as The Flash and Barry Allen as the Green Arrow. "Elseworlds" also introduces a new timeline, Earth-90, which incorporates John Wesley Shipp's Barry Allen from the 1990 The Flash TV series into the Arrowverse.
Season 5 of The Flash returns Tuesday, January 15, 2019, followed by Season 4 of Supergirl on Sunday, January 20, 2019, and season 7 of Arrow on Monday, January 21, 2019.