I contacted the team responsible for invoicing at the Ariba Network. Companies may have a variety of information needs and the method to collect information can vary, but the Ariba Services team can help to configure the Ariba Network to align with any approach.
Here's a link to an article at Ariba Connect that addresses this topic:
I hope this information helps.
Ariba Exchange Community Manager
So what level of effort is needed to map these accounting fields from AN to Ariba Invoicing, once the Invoice lands into Ariba Invoicing via AN? We want to see the accounting that was entered by the Supplier on the AN, in the Ariba Invoicing.
You'll need to work with the Ariba Services team. Customers and their integration partners cannot do this type of customization independently. If you need assistance connecting with Ariba Services, our Partner Support team can assist. You can contact the team at SRMCloudEnablement_PartnerSupport@sap.com.