Apparently there are different types of esters. I'm not claiming to know enough about it though, but Speediagnostix recently posted a high mileage video where he talks about this.
and
Here he shows graphs of the Pennzoil Platinum, High Mileage, and Ultra Platinum oils, including two different ester spikes. At the 6:10 mark of this video, he talks about this. He says the ester used for seal conditioning in the high mileage oil is different than the ester used in Ultra Platinum. He conjectures the ester in PUP is a Borate Ester.