Well, I think I found the answer to my question on the Epiphone Talk forum:
"The new Epiphone P-90 PRO™ single coil pickups are also made with 18% Nickel Silver covers and have been designed and tooled from the ground up with new bobbins manufactured to historic dimensions, Elektrisola magnet wire, sand cast Alnico V magnets, and pole shoes manufactured using correct alloys and to Gibson dimensions. And for you sticklers to detail, the new Epiphone P-90 PROs™ also have tin plated brass base plates like used on 50's and 60's era Gibson P-90 pickups."