Apple returns on unused replacement parts?

I recently "lost" the right earbud of my AirPods Pro and requested a replacement. Apple treats this as a DIY replacement part rather than as a device purchase. Before it arrived, I located the lost piece. I received the Apple part and didn't open the box, and I was surprised that it refuses to accept a return. I've done an exhaustive web search and could not find a stated policy about not accepting unopened DIY repair parts. The refusal of a major manufacturer and retailer not taking a return on an unused item or prominently notifying customers of its no-return policy are unacceptable. I gather than Apple's DIY program is still fairly new. Could they just be setting up their policies and procedures?