Where the Revision History section in the EFR/EFM family datasheets describe all of the changes, they all appear to relate to updating tables and documented specifications. Every few revisions the ordering table is updated to new revision OPNs. Is there an actual silicon difference between the part revisions, or is it more a matter of improved characterization, and that the later revisions indicate conformance to the revised performance spec based on the improved characterization?
You could take a look at the errata to know the die change.
Take the EFM32GG as example, you could get the errata here.