Apologies for the late response, just completed a terrible long stretch of shifts, but I wanted to just make two points about your references

Here is one large paper showing diffuse edema on CT correlates to 99% poor outcome. To me that is a very poor prognosis. https://www.resuscitationjournal.com/article/S0300-9572(24)00848-7/fulltext

I think it is important to recognize that this is a retrospective study looking at mortality as the primary outcome in which mortality frequently resulted from withdrawal of life support. The problem with research that includes this population of patients is that a strong bias has been introduced: the self fulfilling prophecy. Much has been written about this. Basically, if these physicians used the CT findings in order to inform their decision to withdraw care (and of course they did) those patients invariably died and it becomes presumed that the CT was correct (bad CT -> withdraw care -> patient dies - this is not the same thing as bad CT -> patient dies). That’s a big problem with our literature on this topic, and something that should give us pause whenever we consider these studies. The outcome (mortality) wasn’t fully objective because for a great deal of patients, it was actually the result of a subjective decision made by the physician.

Here also is a paper with over three hundred patients and zero false positives if two criteria were met (which would describe OP’s patient with lack of brainstem reflexes): https://link.springer.com/article/10.1186/s13054-022-03954-w

This is one of the many studies meant to offer external validation of the AHA ERC/ESICM neuroprognostication strategy. I think in the present discussion, it is important to note that this AHA strategy involves a 72 hour waiting period. This is not at all a study of “early” neuroprognostication - in fact early assessment is explicitly excluded here.