You seem to have gathered some info. on the subject, what would be normal incidence? And yes, articles were about two different things by design so one doesn’t refute or challenge the other.
I had a grandparent die of ALS so I have particular interest in the subject - it’s a particularly horrible way to die, and having a family member with the disease is a significant risk factor. Normal incidence is about 2/100k population, in Gulf War vets the incidence is about twice that.
http://www.neurology.org/cgi/content/abstract/61/6/750