How do we REALLY think we REALLY know?

Crater impact age is more determinable on the moon compared to earth because earth still undergoes weathering and erosion processes that recycle the oldest of materials. On the moon however, very little, if any occurs. The rims may have some weathering due to additional impacts, but for the most part what was there then when moon was in a major bombardment stage, it is there now.
Though, it does bug me a bit that up until a decade or so ago, we realized that the moon's rock samples and other data collections were localized to the near side and major impact craters.  This definitely limits the scientific data and opens our critical thinking hypotheses.
Why do they believe that the meteorites found in Antartica and other Southern Hemisphere areas came from the moon? And were different composition than what the Apollo Missions collected?  Is is because Antarctica is not populated except by those penguins and a few brave souls?