I have an early 1969, and the one on the right (below) is what's on the car. However, this car is a mystery and much of the car seems to have been reworked and/or replaced. The rear valance is one of those areas, so I don't trust that these were original to my particular car. There are lots of 69's on the interweb with both thick and thin style. Was this a mid-year change?
NPD link to what they call the "later thick style that protrudes from the housing":
LENS, BACK UP LIGHT - #15514-2A - National Parts Depot