The one real risk is that it’s a respiratory depressant and that it’s LD 50 is only a few tens of times a standard dose

The article claims it's much closer than that:

Experts and festival-goers agreed on the likely cause of GHB's disproportionate overdose burden.

"As little as 1 millilitre difference can tip you from what you're looking for to what you're not looking for," Daniel Fatovich, chief investigator of EDNA, told Hack.

I tried to find some stuff to back this up. The "therapeutic index" is probably what I'm after (ratio of effective dose to dangerous dose), despite this technically not being a therapeutic use.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8843350/ - The narrow therapeutic index of GHB renders its use hazardous with poisoning or toxicity not uncommon with small titration of doses.

Thats... annoyingly nonspecific. A number for the T.I. would be a good educational tool.

This paper claims its around 5:1 to 8:1:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4462042/ - Mortality rates after abuse of GHB are high, because there is only a narrow safety margin between a recreational dose and a fatal dose, which is only 5:1 to 8:1 [4-8]. Accordingly, accidental poisoning after recreational use of GHB is not uncommon as evidenced by admissions to hospital emergency departments for treatment [9, 10] and during forensic medical investigations of drug intoxication deaths [11-14].

Someone else in the comments here mentioned that the recreational dosage for different individuals varies, if that's true then it could make this worse.

polydrug using who get hurt [...] education if we want to save lives

Agreed. Most people don't understand what's in pills they have bought or the interactions with alcohol.