Regarding earnings for YouTube ad revenue, partners should reference their earnings statements from PayPal to document income if PayPal was how payments were received (no 1099 or W2 is sent in that scenario). The only exception would be if your channel received more than $20,000 in payments and you received over 200 separate payments during a calendar year through PayPal, in which case PayPal would provide a 1099 (please contact PayPal support if you have questions regarding that rule).
For partners who did not use PayPal to receive payments (who were paid by check or direct deposit, as an example) and earned at least $600 in 2016, 1099 forms should arrive by February 28 (those earning less than $600 do not receive a 1099 or W2).
Additional note: If you had any brand/integration deals through Fullscreen in 2016 that were paid by check or direct deposit, then 1099's for those deals should be received by February 28. If you had any brand deals outside of Fullscreen, then the brand would send you a 1099 directly. (Please note that brand deals are not Influencer Plus campaigns. If you don't know what a brand deal is, then it's likely you didn't have one.)