This Planetary Society article explains how crater density per unit area on the lunar surface helps identify what regions are older/younger than others. It also mentions that this chronology can be used as a basis for the chronology across the rest of the solar system.
Is this methodology accurate? I understand that there aren't many alternatives at the moment, but can we really assume that regions on the Moon and (say) Mars with a similar crater density were struck at around the same time? How can we verify that these craters weren't simply formed by two temporally distant different events with a similar impact density?
The article linked above explicitly says that crater counting on the Moon acts as basis for chronology for other bodies:
That's the lunar crater chronology: The spatial density of craters larger than a standard size versus radiometric age (we use 1 km as that standard size). This crater chronology is then scaled and used as a basis for the chronology across the rest of the solar system. When you hear someone say that something on the surface of Mars is X number of years old, chances are that's based on the lunar samples from the 1960s and 70s and the crater counting done 40 years ago.
My question is about crater couting for relative chronology between celestial bodies - is it really reliable? I guess it's the best we can do at the moment.