It will actually surprise me if SI doesn't send 1099s this year to those who earn over $600 because the corporate owner of them is, I believe, now a US resident corporation. But they may be using a corporate structure that presents them as a wholly owned foreign subsidiary.
Whether you get a 1099 or not, every cent paid to you will be reflected on the company return as part of their expenses. Should they be audited, they may need to prove their expenses and that leads back to you. A higher percentage of businesses get audited than individuals and you want your shop sheets to provide your backup of wht you were paid, whether it was reimbursement or fees, and have claimed it on your Schedule C.
I do not print their invoices as my records with them are reconciled every month with payments and my records show a lot more information than their invoice.