Upgrading systems w\ the pre-RPM installation to RPM based (without sufficient cleaning) fails. By itself, not a significant problem - but will need to test (and may need to fix things) the scenario of upgrading from one RPM version to another (without requiring a fresh system). The question isn't if RPM supports that, but if the RPM spec used is doing it correctly.
Upgrading systems w\ the pre-RPM installation to RPM based (without sufficient cleaning) fails. By itself, not a significant problem - but will need to test (and may need to fix things) the scenario of upgrading from one RPM version to another (without requiring a fresh system). The question isn't if RPM supports that, but if the RPM spec used is doing it correctly.