How to setup corporate card programs

We have a requirement where we are using 2 BU for same country. Now we have 2 different card program for both the BU. We have some employee which recently migrated from Bu1 to Bu2. When we are getting Amex CC trxns loaded into system the card program getting assigned to them is for old BU. Also balancing segment for them is from old company. Our expectation was that employees new CC program should have picked up as BU is changed. How can this made to work. We have made matching rule as employee number.