First off, you have a proto-lanet whose consolidation is interupted about 3.8 Gya, leading to the Late Period Bombardment Events. The fragments then fall in over time, but at a decreasing rate as this pool is exhausted.

You also have a constant stream of comets coming inbound, someof which are captured into the resulting gap, and then leaving later - the assumption here is that the Oort Cloud supply remains comstant, which is not a very good assumption - the supply has to diminish at some indeterminate rate -

Those cpatured will loose volatiles and further condense while captured, and this should show up as some kind of regular distribution among the Carbonaceous Chondrite population -

ep