Why does the changed credit days not reflect in the Sales order ?

Cause:
Sales order entry done prior to change in Customer Series credit update . Customer series changed by user an hour after Sales order is entered.
So credit term pick up by system which was as earlier in the master. Sometimes a new series is defined and not mapped with the credit term in Customer Series Credit master. So credit term is not picked up by the system.
Suggestions:
Users need to enter the Sales order after the credit term policy is saved and mapped in customer series credit. If a new series is created then the credit days will reflect only when the series is mapped with the credit terms in customer series credit.
Users can check in new product Sales orders . Credit days reflecting properly.