“The ice was where the ice was and we can tell where it was because it leaves scrapes and other markers.”
You sure it’s not more of a case of one area being better surveyed than the other?
Without a time machine equipped with a video camera, the indications of proof are not perfect. But this is not a problem that only scientists have to deal with. Historians and even biblical scholars have no video, either. Who's to say that Cleopatra or even Jesus existed?
When you have all the evidence you can find and it's uncontroverted, you make a conclusion.
That's only reasonable.