For the newer USB-PD modes, you also need to know the maximum safe voltage (and related construction features, such as CC pins being a bit shorter to enable a safe/spark-free connection teardown), or you risk arcing.
AFAIK all cables are de-facto rated up to 30V, as you won't save money if you make insulation even thinner. So this is non issue in practice. Plus you can't really measure breakdown voltage without destroying the cable.
And I think one important feature is having shorter CC pins in the connector, so that the power source can shut down the high voltage to avoid arcing altogether. That seems to be a feature distinct from insulation.
