I think I read it in the PpH that a handful of cases where death didn't occur for over 12 hours were due to alcohol and opiate addiction, which made the liver super-efficient at processing large amounts of toxins in the first place.
Again, non-discovery is the key. Most failures of N documented here were due to early discovery (i.e. within the first 12 hours).
Most of the data is collected from legal organisations such as Exit/Pegasos. Bear in mind that they are despatching the already frail, cancerous and elderly.
Even in the Louis Theroux documentary about MAID in CA, the dude was in his 70's, thin AF, legally obtained 15g of powered N and took 8 hours to die, with a doctor, who was a family friend, expressing concerns after 5 hours that the dude might regain consciousness after many hours of agonal breathing.
As a relatively healthy, 260 pound hard drinking 50-something year old, it's either three bottles of N or a whale-harpoon to the skull for me. I'd prefer the former option.