IMHO WildFly is not responsible for the message codes of components it consumes.
If Artemis had two messages with the same code, and it changed the code for one to correct the duplication, there's nothing wrong with that. WildFly doesn't guarantee bug-for-bug compatibility across releases so I don't see why Artemis should.
If it took a code and re-used it for some other message unrelated to its previous use(s), well that's not good but IMO not something WF can try and correct.
If it completely reworked its message code scheme, well we did too in WF 8. And again not something we can try and correct.