So when you are writing a story or comic you always want to get your audience of how the story is in the same universe if its an easter egg character or city or the reference you get and might have heard of before or trying to make sure that the story itself is different before even having another one with the characters from before already in the same universe.
Different characters would need who they are based on any other characters or inspired by the likes of Superman Captain America Iron Man Batman Wonder Woman Green Lantern Martian Manhunter etc. Or want to have a Special Forces that is set in an unknown universe but set in the same one that you created and explain who they are and where they came from if not then leave a know unknown history which we may know or not.
If the story is about the dangers of war or alien forces from outer space coming to the planet and who they could be and are a threat to humanity and national security risk or access to the deadly weapons. Or a villain is formed and ready to take over the country or the world with an iron fist and spread fear across the nation if he is looking for a survivor of their race and was well hidden for a long time and they didn't know about it until the 21st century. After the conflicts and now the world is aware of all their activities and now that us government looks over their race technology and ships or warcraft transportation study it and keep it under a secure location or maybe in a tight security control and then you end a story with a saying or maybe someone you know or don't know watches and believe that it will be time before another threat comes and then you have the figure from before in the same story where now the dots are connected.