But there's no way to test it (at least without time machines and sundiver ships, which we can't prove are possible) so the logical positivists would dismiss it as nonsense.

Objection! We don't know that there's no way to test it. And if we do presume that to be the case, then there are no differences between cake-formed-in-sun and cake-didn't-form-in-sun - no differences whatsoever, since even a single one would permit a test to distinguish between the two.

If "X happened" and "X didn't happen" have exactly the same consequences, they describe exactly the same thing, and thus "X" is meaningless. If we imagine that "X happened" really does have consequences if something else also happened, and that thing didn't occur, talking about X is now pointless.