The GE bulbs are just dated with month-year so 4 68 is April of 1968. When considering which type is correct, GE or Westinghouse, you need to think about WHERE your car was built. I have had a bunch of Lynch road cars and they all seem to be Westinghouse. This would include Superbirds. St. Louis cars seem to all be GE. All the musclecar area bulbs would be the wide flute design. I think the narrow flute didn't appear until 73-74 era. Also it is just needless to search for proper date codes as they are only ink stamped on the backside and you can't tell a 1965 bulb from a 1971 on the front side.