IDOC segment in INVOIC01 to handle product certification date

I am currently mapping some requirements for an interface between an EDI vendor and a customer, the EDI vendor has a special invoice mapping for pharmaceutical companies, they have a field in the mapping specification called ''product certification date' the idoc message we are trying to send is an outbound invoice document by the way based on INVOIC01
I have checked the entire documentation in WE60 for INVOIC01 and cannot seem to find any IDOC segment to handle this requirement or even suitable qualifiers

Anyone has any pointers?

Thanks