It
is always better to wait until you have received all your tax forms before
filing your tax return. March 15th may seem late, but your tax return isn't even due until April 18th 2017.
The IRS receives copies of the same 1099s (as well as other forms such as W-2s, W-2Gs, 1099-INT, etc...) that you
receive. They will compare your tax return to the 1099s (or just the one) that
were (was) reported to them. If the income reported on your tax return is less
than the income reported to them on the 1099s, you'll get a notice from the IRS
that states that you owe them taxes for the income you did not report.
If you have already filed your tax return, you will have to amend your 2016 tax return to include the investing statement income. You can not include a prior years tax document in the current years tax return. Each year stands on its own.
