What date do you get when you add 1 year to 29 February 2020?

The answer has to be dependent on the domain you’re working in.

If you’re calculating product warranties, it’s in the best interest of the business to end up at 1 March 2021 - people will be delighted to find the extra day of coverage, if they need it. Going the other way might reduce your theoretical liability (making the bean counters happy), but that would be at the cost of negative publicity.

In a different domain, however, you want to go the other way. Say you’re working out when to release someone from prison - why not err on the side of mercy?

Also look at th eother side of the calculation - if you’re working with a date calculation that lands on 28 Feb or 1 March, should you slide to 29 feb?