[samatman]

This has been a factor in contract law for longer than computers have existed. "Subtract a year" or "Add a year" aren't really imprecise, it's just that there are two ways you can interpret it: 365 days, or 12 months. When adding, you get the same result: end of February, the 28th. Subtracting, you get one of March 1st for 365 days and February 28th for 12 months.

Most jurisdictions use the 12 month standard, fwiw. I believe that's the ISO ruling as well, but I wasn't able to confirm that.

[emmelaich]

Which type of year? Sidereal or solar? Did you account for axial precession?

[samatman]

To be a bit blunt, these questions are entirely irrelevant, since you know the answer as well as I do: the calendar year, the one Western law and international business uses uniformly. It's very clever of you to mention that other concepts of the year exist. Kind of. Would have been more clever if you'd realized that they aren't germane, any more than the Islamic, Jewish, Indian, or Chinese years are.