This mod was done many years ago, before it was common to be able to find someone who could do proper frequency response measurement. Unless someone measured them in the thread, I wouldn’t assume the visual difference check identified 100% of the differences, including material differences.

Sennheiser likes to reuse parts across their headphones lineup. They have several current models that look similar despite tiny internal differences but have substantially difference frequency response due to those tiny changes.

This is always going to anger the people who think the cost of objects should be based solely on the cost of materials. I find that especially ironic for a a website where most of us work on software products where the cost of running and distributing the software is vanishingly small and produces margins these hardware companies could only dream of.