Considering the similarity in action of both, the symptoms can be rather the same but only Nitrite has a deadlier outcome at far lower dosages and with how rapidly it works. I think its happened more times than not on this forum especially due to how some people are still conscious after an hour or so and especially having not vomited but in other cases, medically speaking, people have still rapidly deteriorated after taking sn more so than with Nitrate. While Nitrate can also kill, it may take higher doses to get anywhere near fatal levels while SN, as we've seen, can take serious effect at 2 grams and may already need medical intervention depending how symptoms progress. This is why immediate medical intervention is repeatedly stated as the only thing that can save anyone especially since Methlyne Blue is the most effective antidote. On top of this, in the case of severe Methemoglobinemia, even if a timely diagnosis is made, the management of such severity is still challenging regardless of whether M-Blue is available or not and this is why, in some medical cases, like this
one where one individual ingested 18g, he still died even with aggressive resuscitation, it's even further complicated in the event of Out of hospital cardiac arrest, CPR or hypoxemia-reperfusion injury.
This is why SN is really deadly and those that called for help which is the major reason why this method is unsuccessful are very fortunate because they called early enough before the methb levels progressed in severity, in reality, they could've still died if they waited a minute longer, that could've made all the difference.