I just upgraded DCRUM 12.2.2 to version 12.3.5 and this appears in the DMI section of type "Interactive table and chart" for migrated DMI reports. If you create a new DMI report using this type of DMI section in a CAS v. 12.3 the dimension is "Tier".
We upgraded DCRUM 12.2.1 to 12.3.5 and I can see the attached "(obsolete)" at other dimensions in migrated/updated reports, too. E.g. DMI Report --> Drilldown links
... but the drilldowns seem to work anyway.