[Jasonft]

Would travel near or even over Alaska/ Russia jump worlds? This could have lead to some very interesting wartime confusions once air travel and radio communications become the norm.

Likewise underwater travel. A submarine killing the 'same' ship more than once is entirely possible.

The level of confusion once things start breaking down will be immense. Once people start to get a clue the ocean floor out there is going to be intensely studied by the out-timers while the locals start thoroughly losing their minds.