It is always better to wait until you have received all your tax forms before filing your tax return. 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.