I remember reading about a story[1] last summer of a user on reddit buying a box full of "Blizzard stuff" on eBay and in it he found a gold cd-rom that was the master source code disk for Starcraft -- this wasn't even a hand-written label type thing either, it was ink-or-laser jet printed and had a custom sleeve and all. How does something like that end up in a box of junk for sale on eBay... crazy world. I think he ended up not ripping the contents, to the chagrin of many (including people advocating for source archival, but who knows how many were just using that as a cover and what they really wanted was to cheat at the game), and sending it back to blizzard and I think they flew him out to their game conference as a thank you.
Just this past week, a number of classified government documents were obtained by reporters in Australia - in that case a filing cabinet had been sold off as second-hand, still containing government files[1].
The investigation into how this could happen is still ongoing, but the reason that's been reported so far is that someone just lost the keys.
If something like that can happen to government documents, just imagine what could happen to general company assets.
1: https://kotaku.com/guy-finds-starcraft-source-code-and-retur...
EDIT: found the story, and i was wrong about the sleeve looks like it was a regular jewel case, but still.