The numbers on that site aren't quite right. For the Pixel 8a, May 14th, 2031 is 2036 days from now which is ~5.58 years rather than 5 years. They're using the 1st of the month instead of the launch day and for some reason the number of months is also sometimes dropped. In practice, a Pixel being launched in May will mean it's going to get a final update in May and the first missed update will be June rather than May. That means their end dates are 1 month early in practice. Not clear why the number of months gets dropped for some of the values they show such as the Pixel 8a.