Of my 500 or so records on CD or vinyl there are a lot of mediocre albums that I like a couple songs off of, or I have to be a completest with a band. I don't see selling any of them, just not in my nature.

I was once a completist. Then I went through a period where I moved 6 or 7 times in 5 years.

I reached the conclusion that my life was made worse, not better, by owning hard copies of Cryptic Writings and No Prayer for the Dying.

Same for me here, and I'm close to 6900 items.
Bands like Siculicide, Bathomet... Wrong purchases. But they're here, and will never leave. I only sell/trade double copies because I bought twice the items mostly because I didn't remember I already owned it