They were all made in the same place. They all had a seperate inked in number on the base plate in addition to the stamped patent number.
The first three digits will tell you the type. 137 is a neck pickup with less windings and 138 is a bridge pickup with more windings. There is a date code after the fist three digits. 1381280 would be a bridge Shaw made in December 1980. Not all of them had the silver PAF sticker.
They had PAF coilforms with the square/round inspection holes and no T on top. The wire is a bright copper color. The magnet was a special Alnico V that was longer like the 50's style and rough cast. This is a special magnet and the closest to a vintage PAF in tone to my ears. They had white plastic spacers and braided connecting wire.
They typicaly read under 8Kohms and seem to average out in the middle 7's. They sound very big and powerful in spite of the low readings.