You have to claim the education expenses and apply for the education credits in the tax year that they were paid.
In your situation, you would report the 2016 1098-T on your 2016 tax year return, but you would need to amend your other tax years to report the 2014 and 2015 1098-T's.
The education credits can be valuable, so it might be worth it for you to file amended returns for those years if you are eligible for any of the credits.
Below are links with more information about education credits and filing amended returns.
CLICK
HERE for IRS Pub 970 Tax Benefits for Education
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