Thanks to Len at biodiversityforum for pointing out the difference between cranial index (dry cranium) and index of living humans (cephalic index). This is what you get when you're an amateur...
So the stricter values of under 75 (dolichocranial), 75-79.9 (mesocranial), over 80 (brachycranial) and 85-89.9 (hyperbrachycranial) are for dry cranium and represent cranial indexes.
And the cephalic indexes for living humans are the one's mentioned earlier Dolichocephalic x- 75.9, Mesocephalic 76-80.9, Brachycephalic 81-85.4 and Hyperbrachycephalic 85.5-x.
So the point is that there's no real use in re-calculating the existing data into a stricter system, since the subjects of the studies were all living people.