I recall that post-mortem procedures were not carried out in many of the cases. I don't know if Sux is one of the routine poisons/substances tested for in PM's when an unexpected/unexplained death happens in hospital.
It is possible that intubation procedures took place as a clinical need but against laid down protocol, due to understaffing and poor working practices/lack of supervision. Errors in establishing the correct dose for the patient could occur in the pre-intubation medicinal procedure.
I have first hand experience of investigating such an occurrence in a hospital, owing to shortages of appropriately trained staff on a night shift, when junior staff operated outside of laid down protocols, to get the job done! I would not be surprised if it has been a common occurrence for a long time.
Succinylcholine: Is It the Perfect Murder Weapon? Not Exactly.
All my own opinion, of course.