2020 1099 3-Up Double-Window Envelope (Stub On). Ensure immediate attention! Double-window envelopes come preprinted with the statement Important Tax Return Document Enclosed . Compatibility: Use with Continuous and Laser 1099, 1098, 5498 and W-2G forms (except 1099MISC & 1099R) with right stub ... - 2020 1099 3-Up Double-Window Envelope (Stub On).