Retired to Win, you have mentioned that this questions is more towards those in their late 60's, but then you continue to query and push those who are sub 40 years old. Retiring in your late 50's or early 60's, I believe when you decided to retire, is completely different from someone doing a One More Year when they are sub 40.
Many of those who are sub 40, can't fully grasp how their expenses for kids, health, and other areas are going to significantly change in the future. If your kids are out of the house and your expenses are stable then it is easier to project your needed amount. You also retired with much more certainty regarding Social Security and other pensions. This is completely different from someone who only has 10 or so years of full employment. Their Social Security is permanently effected by retiring without having 35 high years of compensation. This can be done, but everyone had better have a strong understanding of their desired spending in the future and have safety built into their Stache. A professional that is getting a premium for their knowledge may be stuck with minimum wage 20 years after retiring. Doing one or two years "extra" can almost guarantee success with the worst case that you leave more money to charities or family. They would most likely still be retiring 30+ years earlier than "normal" retirement. If your job is completely miserable, then it might be time to find a different job vs. retiring at the minimum of the spectrum.
You also mention lifespan vs. safety. If you are retiring at 35, your lifespan is somewhere in the 82 year range. Giving up one year for increased security and safety is giving up 2% of your remaining life. If you are 67, you have 19 years of life remaining, so you are giving up 5% of your life to increase your security, when most of your life and major expenses are behind you and your Social Security income is probably locked down at close to the max. In my mind they are different scenarios for One More Year syndrome. Those who are 40 years or less are gaining knowledge and wisdom by staying put. That extra year can be used to reflect on your values, get a better understanding of your current expenses, figure out your future expenses, and increase your safety margins. Like most thing Mustachian, the goal is to spend your time and money on areas that improve your life. That one extra year may give you the security and confidence to know that your life is set and you have a clear vision for the future.
Thanks for the question,
Tom