Scenario concept: over time

OK, so I have been thinking about the idea of a scenario that reuses the same topography with a linked narrative over time. Let me give you an example of what I'm talking about, on a three-scenario model. I've decided that this is a miniatures game scenario, using one of my current favourite games, the Cthulhu skirmish system Strange Aeons.

For many and good reasons, my campaign is set in the UK, but it's just an example; and you could easily do something similar in another setting.

Scenario 1: It's the 890s AD, and a group of Vikings are raiding an English village, only to find out they've bitten off more than they can chew. The natives turn out to be allied with sinister fish-folk, and the Vikings have to fight their way out. (I have an appropriate collection of models for this scenario.)

Scenario 2: It's the 17th century, and a local witch is making a last stand against a witch-hunting mob. She summons up the skeletons of the dead Vikings to defend her witchity hovel.

Scenario 3: It's the 1920s, and a team of archaeologists are excavating the site of the village church (or the burial mound of the Vikings, or something; I haven't got this one sorted out yet). They awaken some kind of horrible evil, the usual.

The question is: how do you make each scenario affect the subsequent ones. Like, the witch might get more bennies if she has the skeletons of particularly tough Vikings to use -- that's a good one. But for the rest, I am unsure.

Encore le swipe file

• A kingdom with a disputed succession is ruled by a council consisting of the rival claimants. 
• The way to complete a magical thingamabob is to walk a labyrinth. 
• A shapeshifter has no identity without a form to shift into. 
• A band of soldiers are led by a young child who is technically a prince. 
• A charismatic leader inspires fanatical loyalty, but his subordinates detest each other. 
• A window into another dimension only works when placed at the corresponding location.

Actual content soon, I promise!

The swipe file again

• Hovels or nests are made from the fine silks and other luxury goods of a wealthy city. 
• A dungeon's map is based on a building's floorplan, but turned to an incorrect orientation.
• An occupying army has gone batshit crazy native trying to "maintain order."
• A new weapon or fighting style appears to the natives as some weird monster.
• Several different NPCs turn out to be the same person in disguise. 
• An empire's royal family are a completely different species. 
• Half-elvenness is contagious.