User blog comment:ReverseZoom101/"Crisis On Earth-X" Plotholes and Easter Eggs!/@comment-3221148-20171210201445

Plot holes are contradictory elements within the story, not "events we are given no official explanation of". Maybe Oliver asked some alternate universe Wells to get him Kryptonite, or phoned Bruce Wayne to ask if he has some. Kara has fought Dominators in her own universe last year, regardless of Barry's "fuck ups". And as for the number of Earths? Maybe Kara had a multiverse study class on Krypton! Maybe Harry Wells was proud to discover another one! But, hey now, Red Tornado has just stated in Freedom Fighters: The Ray that there are actually THOUSANDS of alternate universes, whaddayaknow!

"Not fully explained backstories" are not plot holes. Eobard Thawne had many off-screen adventures, for example, including a whole alternate campaign against the Legends which killed them all except for Rex Tyler.