I DOn't know much of the reason but many MIJ guitars before 80 have MOP markers. Expensive ones like my Burny dove BD-80 but also unexpensive ones like Matsumoku epiphone accoustics, or my Greco EG-550C from 1975. My Burny dove is from 78 but I4 tried others from 1980 and if I remeber well, they were acrilycs markers.