A good question, and your numbers might be mostly correct, but there are some false assumptions leading to them (based on the information presented). Just because 40 years ago there was a 67% vote to join, that doesn't mean 67% of the people that voted to join are still alive (that assumes the voting results were fairly uniform across age demographics. It could be that young voters voted predominantly one way and older voters another back in 1975 (as it is reported they did now). That could greatly raise or lower the percentage of people still alive that voted to join.