It doesn't matter when it comes to responsibility.
But if you want to judge them, then I think it's relevant. Because just about every company is susceptible to an errant employee causing damage in some way or other. So do we want to judge companies on their policies and overall damage rate and probability ("how likely am I to suffer this fate if I do business with them, and what is it likely to cost me?"), or on whether they won or lost the errant employee going viral lottery ("did a bad employee work for this company once and cause damage in a way that happened by chance to become very public")?
But if you want to judge them, then I think it's relevant. Because just about every company is susceptible to an errant employee causing damage in some way or other. So do we want to judge companies on their policies and overall damage rate and probability ("how likely am I to suffer this fate if I do business with them, and what is it likely to cost me?"), or on whether they won or lost the errant employee going viral lottery ("did a bad employee work for this company once and cause damage in a way that happened by chance to become very public")?