Since many of QuickBooks Online users are using Mac computers if your import file within Transaction Pro shows a diferent date please refer to the info below submitted by a user, Nearly Digital:
Did your workbook originate on a Mac? If so, or even if not - check to make sure that the 1904 Date Format is not turned on. This will cause a constant shift of 1462 days.
The excel setting is in different places depending on the version, in Office 2010 its in "Advanced". I just turned it off myself to fix a similar issue (workbook sent to me from a mac user). If this is the problem for you you will see that now you have to use a formula to re-increment all of your old dates because they will all be early by 1462 days.
I haven't a clue why Mac defaults to this, it has caused me headaches before in a mixed environment. I'm just speculating its a Mac related issue, as this is when I've seen it turn up the most - your issue could be unrelated.