A few years ago I was doing an upgrade to an ERP system.
All seemed to be working fine. About two weeks before go-live UAT testing started. All of a sudden there was a massive uproar as a key piece of functionality had completely gone AWOL, all associated tables and code.
Much head scratching on our side as there were no errors in the logs and everything had gone really well up to that point.
So we cross referenced the production system still on the older release, traced the functionality only to find none of the tables/programs where marked as vendor specific code or even customer specific code.
After much digging we found out that the Vendor had demo'd some beta code on their system but it was never purchased.
Some bright spark then decided (contractor), to export the tables/programs from the demo system and import it all into the normal DEV/QA/Prod landscape, passing it off as his own code, so had managed to "save" the company a stack of cash for the functionality they needed.
Alas as the code was not signed correctly it got deleted on the upgrade.
Much embarrassment later they had to hand over vast amounts of cash to the vendor (backdated licences for 5 years), the go-live date was missed due to having to import the official code base, create routines to export the data and reload, and do another round of regression testing.