400 and 430 is not the same
The 400 years given in Genesis 15:13-16 and the 430 years given in Exodus 12:40-42 should not be clustered into the same event but rather separate events. To begin with, they do not represent the same amount of time. There is a 30-year discrepancy between the two. In addition, each duration represented an entirely different endpoint.
The Genesis time cluster of 400 years started when God made the covenant with Abraham and continued until Israel entered the Promised Land. The 430 years mentioned in Exodus marked the 430th anniversary from the day Abraham left his hometown of Ur to the Exodus from Egypt.
The covenant between Abraham and God in Genesis 15:13-16 was one event that started with God’s promise and was fulfilled with Israel’s arrival in the Promised Land. Exodus 12:40-42 is a timeframe marking the duration between Abraham’s departure from Ur to the Children of Israel’s departure from Egypt.