Correct, in the event of a collapse of civilization record might be lost.
But under such a scenario, how would some future civilization get contaminated? What are the chances that they'd dig hundreds of meters deep in an area with no valuable resources? The proposed scenarios in which nuclear waste may harm humans far into the future are exceptionally unlikely. Contrast the remote possibility of this form of harm with the millions that die each year due to fossil fuel pollution (and many more that may be harmed by climate change).