Headlight bulb supplier

I have four 1965 Darts. The three Dart Chargers assembled in December and January all had GE bulbs. My 270 wagon assembled in June 65 had GE bulbs as well. However my old 270 wagon that I parted out due to rust issues had GE and Westinghouse. Assembled in April 65.

This is facts. There is nothing mentione in the partsbook. @slantsixdan might have some more details since he is the pro here.