On upgrade, the KnativeServing currently says:
Could not add knative-serving to SMMR. Please refer to the release notes of Openshift Serverless 1.2.0 for more information on how to resolve this
That's not helpful enough. We should say something like

Could not add 'knative-serving' to SMMR as it's already part of another SMMR, likely one in 'istio-system'. Remove 'knative-serving' and all namespaces that contain Knative Services from that other SMMR