>I really doubt that many of those genuine repair parts for iphones and macbooks are stolen, in the sense that somebody loaded up a pallet and took it from its manufacturer without paying. Apple doesn't manufacture most of these things, particularly the ICs and screens, and relies on a whole ecosystem of vendors and subcontractors.

Theft is much broader than that. When apple receives devices that it cannot repair anymore it will just recycle the materials and throw the rest away, there are employees that will take out functioning chips or broken circuit boards and throw them in a publicly accessible garbage container only to come back at night to take the parts out of the trash to resell them.