The nuance here lies in understanding what curing a jurisdictional defect actually means, and how that doctrine interacts with the concepts of finality and interlocutory orders.
The Court's holding establishes that a jurisdictional defect can be cured only when the curative action is, first, proper, not erroneous, and second, final, not subject to reversal on appeal. In Caterpillar, the defendant was dismissed with consent via a partial final judgment. That dismissal was both correct and final. It established complete diversity, and there was no risk on appeal that the defendant would be restored to the case. The defect was cured before trial, and thus efficiency concerns could justify preserving the post trial verdict.
music for the podcast provided by Dimitry Taras