Do you mean how the ribbon tail is clenched in the eagle's beak, so the beak is shown partially open? I believe the only major design change on the series was for the United States Bicentennial, so I don't think he beak was ever designed differently. There were minor changes to the 1964 proof design to correct some flaws, the original version is referred to as "Accented Hair".
The beak is closed and the end of the ribbon is hanging out of the left side. What do mean by "split"? You may have seen coins in which there isn't much of a distinction between the lower and upper parts of the beak due to weak strikes. When the mint started using copper-nickel clad planchets, you got a lot of weak strikes in the 70s, particularly from the Philly mint. But the design itself didn't change, to my knowledge.
I just wanted to know if there was a visible distinction between upper and lower beaks as I have observed, though my eyes may be playing tricks on me, a slight variance in the beaks. Thanks for the clarification.
