I added details post-Convention but I no longer see that comment on this thread. Here's what was posted after Convention:

Systems Committee recommended changes based on discussion at the 2023 IAIABC Convention-Systems Committee meeting: 
One change is needed: Modify the IAIABC Release 3.1 XML schema for DN0104 Test/Production Code to add the value = D (Development). 

Notes:
DN0104 Test/Production Code of D (Development) will not be added to the IAIABC Release 3.1 standards documentation. Currently there are values of T (Test) and P (Production). 
The value of D (Development) will be added to the IAIABC Release 3.1 XML schema and will only be used internally by a jurisdiction. 
The value of D (Development) will not be sent to the jurisdiction in a IAIABC Release 3.1 XML File or IAIABC Release 3.1 Flat File from the Trading Partner. 
The jurisdiction may set DN0104 Test/Production Code value = D (Development) for internal use on internal applicable files only for either IAIABC XML File or IAIABC Flat File.