Creo que se trata de un formulario fiscal de tipo combinado o compuesto, es decir, que incluye varios documentos de una misma declaración fiscal (= sistema combinado de declaración de impuestos).


En este enlace puede verse que hay diversas variantes del formulario 1099, pero también la opción de presentarlo en forma combinada o compuesta.
http://www.irs.gov/irb/2008-33_IRB/ar08.html
Internal Revenue Bulletin: 2008-33
August 18, 2008
Rev. Proc. 2008-36
General Rules and Specifications for Substitute Forms 1096, 1098, 1099, 5498, W-2G, and 1042-S
Section 4.2 — Composite Statements
4.2.1 Composite Substitute Statements for Certain Forms 1099-INT, 1099-DIV, 1099-MISC, and 1099-S, and for Forms 1099-OID and 1099-PATR
A composite form recipient statement is permitted for reportable payments of interest, dividends, original issue discount, patronage dividends, and royalties (Forms 1099-INT (except for interest reportable under section 6041), 1099-DIV (except for section 404(k) dividends), 1099-MISC or 1099-S (for royalties only), 1099-OID, or 1099-PATR) when one payer is reporting more than one of these payments during a calendar year to the same form recipient. Generally, do not include any other Form 1099 information (for example, 1098 or 1099-A) on a composite statement with the information required on the forms listed in the preceding sentence.
Exception. A filer may include Form 1099-B information on a composite form with the forms listed above.