Tim Gideon said he could hear the difference in his review of the ER4PT at PCMag using some frequency test. He actually rights pretty good reviews so I valued it more than some of the mainstream stuff I'v read. He praises highly the ER4S, owns both and said he could hear the difference.
1. Single examples of the ER4S/ER4PT will have different channel matching just because each unit is slightly different. If they had received a different unit/serial number for review it might have been the other way around.
2. The deviation is mostly above 8 kHz meaning it could be due to insertion depth variation.