Yes, it should have been 5/1/14 for all years. Well, actually only the first year, and other years would not show that at all (but it WOULD show up on the bottom of 8829).
However, it is not a major mistake. You have been missing a $20 deduction each year, but other than that, your mistake didn't really affect much. So I would not bother to amend just to claim a missing $20 deduction. Just start doing it correctly now.
