[alexqgb]

If true, "honest mistake" is an acceptable answer. But it's not one you bring up with the person whose work you appropriated. It's one you bring up with your insurance company when they're following up on the errors and omissions claim (E&O) you filed in order to cover the losses incurred by your own negligence.

Protip: When you're in this situation DO NOT blame an intern. Interns - by definition - are unskilled, unpaid, and uninvested. If your insurance company finds out that interns are the only thing standing between them and damages for an IP lawsuit, they'll strongly consider yanking your insurance altogether, at which point you've got a snowball's chance in hell of finding a distributer.

That's because copyright law allows rights-holders to sue not just the author of the illegally derivative work, but the author's distributors. Since the distributors have no way to be absolutely certain that the authors they buy from have actually cleared every single underlying right, they insist that the authors carry insurance that will cover any losses suffered by the distributer in cases just like this. In any human enterprise, a certain number of errors will happen. That's normal. But if a production company develops a history of recklessness, it may find itself uninsurable, and that's the end of commercial viability.

Handling Rights & Clearances is work that is both skilled and tedious, meaning it should pay well. Employers that "inadvertently" screw artists by cutting this particular corner deserved to get hit as hard as the law allows.