Any comments on these rules? Should I refine them? I'm thinking of making markets like this for other years farther ahead.

Related:

Will Idaho take 10%+ of Oregon’s land before 2030?

11% chance. The Greater Idaho movement proposes that eastern Oregon counties become part of Idaho instead. [image]

When's the last time this happened? (Search engines are failing me.) It's my understanding that the Mississippi River constantly shifts course a little bit, which causes the adjacent borders to wiggle on a semi-regular basis. But I'm not well-calibrated on the frequency or scale of these changes.

The legal border between the US and Mexico is the Rio Grande; but when the river changes its course, the border stays where it was before. This creates parts of one country separated from the rest by the river. It has happened that both Congresses swap land that has definitely moved to the other side of the water, so that the border once again matches the actual river.

So the precise shape of Texas changes.