When Quarkus Core is upgraded from e.g. 2.7.5.Final-redhat to 2.7.6.Final-redhat in the prod Platform and CEQ is present, then the resulting zipped Maven repository should not introduce any new duplicate jar artifacts.

I can see this happening when upgrading from 2.7.5.Final-redhat to 2.7.6.Final-redhat.
See the attached fragment of the surefire report.
Some of those are harmless and inevitable as long as CEQ 2.7.5 was built against Quarkus core 2.7.5 I mean mainly BOMs and parents. I guess those are available in MRRC already anyway.

But still many are serious, i.e. duplicate jars

I think it points at insufficient management somewhere. But I am not able to tell quickly where and how to fix it.