After Earl tells Randy that they were leaving Joy after Earl Jr was born Darnell comes in and he has a wedding ring on. Darnell was not married until he married Joy five years later.
When we first see Earl's gerbils, they are all grey or black. When Earl's dad is carrying the gerbil cage to throw them out the window, all of the gerbils are either white or black, but when he's actually throwing them out the window, each one is honey-colored.