User blog comment:TimeShade/The Crisis Has Arrived/@comment-2054358-20191206062225/@comment-858615-20191211094940

Constantine seems a safe bet, retrospectively. Events from that show have been referred back to, and by now the character's appeared more often in conceived-as-Arrowverse series than in his own show. So it's a little atypical, but it works. That there wasn't actually a lot of material in his own show to start with probably didn't hurt.

CBS Flash? See, I've seen a pretty strong link between these two Flash shows even before Flash-90 showed up on the CW one. (If you squint, CW-Flash looks like 'What if the Flash happened 24 years later?' compared to the CBS one.)