That requirement only exists once the EPA has created the rule. What the 5th Circuit has just said is that if you've been using a hazardous process for a while

That requirement only exists once the EPA has created the rule. What the 5th Circuit has just said is that if you've been using a hazardous process for a while by the time the EPA creates such a rule, even if the EPA and public did not know about it, then SNURs can't be applied. In this case, the EPA tried to regulate PFAS in 2020, but since Inhance had been using them since the 80s (without anyone knowing), the rule was struck down. So any company that begins using a hazardous process is incentivized to keep that secret for long enough that the EPA can no longer create an SNUR regulating it.