They'll need to define their characters' histories at some point. Has it been established whether Barry Allen and Iris are married, post-Death Metal? That's something the writer will need to know. If they ever bring back Patty Spivot, who Barry dated during New 52, then they'll need to establish what their history with each other is. Which stories was Jon Kent around for? When was he actually born? Does it synch up with the ages of other young characters, like Tim Drake? When did Billy Batson become a hero? Which of his origins is in play?