Expect 1912-02-28 is a correct response. The only reason you think the 29th comes into play here is because you remember that the starting point was the 29th. The system has no such memory.
And this is logically wrong because it leads to wrong results. I’m aware that time intervals are difficult to manage but more exactness is needed here: '10 years' must have the same meaning when added to a date and subtracted from it, otherwise it leads to wrong results.
Your suggestion just moves the wrong results to another use case; see my response upthread. There is no objectively correct answer here, like you seem to think.
