This answer is applicable only if your trading partner uses VDA messages (e.g. Ford, Visteon, BMW, VAG etc).
When they start sending new DCIs and Releases using your new Supplier Code, DARWIN will recognise this and will add your new code to the system automatically. Any orders received for this new code can be turned around automatically to create ASNs that will be sent with the new Supplier Code.
If they are still sending DCIs and Releases with the old code, then your order lines will still be linked to the old code because DARWIN has not been told about the new one.
You can confirm the Supplier Code that is being used from the Inbox view in DARWIN Order Processing. The Supplier Code for each DCI and Release will be shown in the "Supplier EDI Code" column.
If this Supplier Code is still the old one, then you will need to contact your trading partner and ask them to start sending messages with the new code. DARWIN is only able to display the contents of the messages that the customer is actually sending.