Question about Bose QuietComfort Earbuds II

I've had these for more than 12 months, no, I'm not familiar with this phenomenon. Do you mean noticeably less output while wearing them or compared to the output for 2 months? I don't mean that in a bad way at all, but analytically, you are sure that your hearing is unchanged?

I have noticed that the volume of the headphones is controlled in 2 ways, they have their own volume control, and then there is the Bluetooth connection.
If you have the headphones set to quiet directly, you can set them to full volume on the mobile and they don't get very loud. Maybe that's it?
Try turning the earbuds up directly. -> simply move your finger from bottom to top. There is a special noise when they are turned all the way up.

I have had the product for 2 years and they are still the same volume. Even when I wear them, they don't suddenly get quieter.