The proof that you submitted them would be your tax return showing that amount in income. If you entered them correctly, the net income or loss from your self-employment would show on line 12 of the 1040 and you would have a Schedule C in your return that shows the relevant income on line 1b. If you entered them incorrectly, the amount could show elsewhere on your 1040 and you would have to look at lines 7-21 to see if there's another line matching the 1099 income amount.