Since the 1940s up until the CNC Router was invented, the playfields were placed into a machine that had repositionable drilling locations. Guessing a type of press that also registered the holes for the playfield screws.
There is a video of this process, done during the late 1970's showing the playfield manufacturing.
images.jpgStern (resized).jpg
This is at Stern, an oldie but a goodie. They could be still using it.