Apparently there have only been two recorded deaths from nutmeg. One was an eight year-old boy who consumed at least two whole nutmegs and the other a college student who consumed 4 tablespoons (28g) of powdered nutmeg.
Although there are cases of much much more nutmeg being consumed that were not lethal. There is one case in historical literature where a pregnant woman consumed 10-12 nutmegs (70-84g) to induce intoxication.
This leads me to hypothesise that perhaps historical nutmegs were smaller, or that they were grown in unoptimal conditions so produced less myristicin.
Transport by ship (probably not in a very good container) could have made a difference, there may also have been changes in the harvesting or drying process in the time since. Storage containers were also likely less well-sealed.
Although there are cases of much much more nutmeg being consumed that were not lethal. There is one case in historical literature where a pregnant woman consumed 10-12 nutmegs (70-84g) to induce intoxication.
This leads me to hypothesise that perhaps historical nutmegs were smaller, or that they were grown in unoptimal conditions so produced less myristicin.