Eddie; I can't tell you if there was a difference between the 69 and 70 assembly line pans.
I do know some late 69's got the second design valve covers with drippers, starting in about August. It would make sense that IF the 1970 Z/28 oil pan was functionally the same, they COULD have started using it early.
I know for certain that the 69 assy line pan has multiple differences from the ones that were sold over the counter starting some time in the 70s.
Comparison is here:
https://www.camaros.net/threads/nos-...l-pans.178450/