When you have a class that implements ArchetypeCatalogFactory and implicitly register another one with the same name using org.jboss.forge.addon.maven.archetype.ArchetypeCatalogFactoryRegistry.addArchetypeCatalogFactory(ArchetypeCatalogFactory), the archetype-list command shows duplicate entries:

 [forge-distribution-2.15.0.Final]$ archetype-list
fabric8 = io.fabric8.forge.camel.commands.project.FabricArchetypeCatalogFactory@bedc1833
camel = io.fabric8.forge.camel.commands.project.CamelArchetypeCatalogFactory@5a0d4b6

Explicit registration should take precedence on existing services, so it should allow easy overriding of archetype catalog factories.