Inconsistency of node-role between newly created vs. long running OpenShift 4 clusters

Issue

• It was found that 4.12 and newly created OpenShift clusters have node-role.kubernetes.io/control-plane label set while 4.11 and older OpenShift cluster only apply node-role.kubernetes.io/master label, even after upgrading to 4.12 or newer. Why this is and how to achieve consistency?
• After the upgrade to OCP 4.12, the control-plane role label on master nodes does not get automatically added.
• While troubleshooting an issue it was found that node-role.kubernetes.io/control-plane was applied on OpenShift installed with version 4.12 while it was missing on a cluster installed with a previous version. Even though both are now running OpenShift 4.12 it's confusing to see such differences and this makes troubleshooting hard.
• Why is node-role.kubernetes.io/control-plane not applied to long running OpenShift clusters after upgrading to 4.12 or newer releases?