Well in the case of TSMC chemical wafer issue it's easier to understand how it kind of went a bit more unnoticed. The degradation might not be immediately noticed, but over time over a period of heating and cooling cycles. Outside of that without knowing their quality control standards it's sort of anyone's guess. They may have tested a initial batch of wafers that checked out fine and a later batch was effected. Both batches though may be part of the initial stock pile of GPU's they shipped since otherwise they get complaints about "paper" launches.
Can you provide any link that contaminated products left the factory? I am unable to locate any such evidence.