I'm doing some Schema changes. I used our existing standard schema as a base, which was already based on 2.3. So let's call our existing one Custom.MHC.Schema (based on 2.3). I created Custom.MHC.Schema.Advanced (based on Custom.MHC.Schema) and copied down one of the code tables then made a change to it.
When I ran a message through, the code table change didn't show up. I noticed in the message viewer that the DocType is still Custom.MHC.Schema:ADT_A01 but the DocType Category is Custom.MHC.Schema.Advanced.