While Configuring [A] OCP cluster to use the resources generated by oc-mirror we apply below commands:
~~~
$ oc apply -f ./oc-mirror-workspace/results-1639608409/
~~~

And to verify that the CatalogSource resources were successfully installed or not we don't need to mention --all-namespace instead we can mention -n openshift-marketplace because 

~~~
$ oc get catalogsource --all-namespaces
~~~

In results-1639608409 catalogsource always point to namespace openshift-marketplace
~~~
$ cat oc-mirror-workspace/results-1639608409/*operator-index.yaml | grep namespace
  namespace: openshift-marketplace
~~~

A. https://docs.openshift.com/container-platform/4.11/installing/disconnected_install/installing-mirroring-disconnected.html#oc-mirror-updating-cluster-manifests_installing-mirroring-disconnected

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    $ oc get catalogsource -n openshift-marketplace