To summarize what the IRS says below, attach to the 1040-X any forms that changed and don't attach forms that didn't.
Assembling Your Return
Assemble any schedules and forms behind Form 1040-X in the order of the "Attachment Sequence No." shown in the upper-right corner of the schedule or form. If you have supporting statements, arrange them in the same order as the schedules or forms they support and attach them last. Don’t attach a copy of your original return, correspondence, or other items unless required to do so.
Attach to the front of Form 1040-X:
A copy of any Form W-2, Form W-2c, or Form 2439, Notice to Shareholder of Undistributed Long-Term Capital Gains, that supports changes made on this return;
A copy of any Form W-2G, Certain Gambling Winnings, or Form 1099-R that supports changes made on this return, but only if tax was withheld; and
A copy of any Form 1042-S, Foreign Person's U.S. Source Income Subject to Withholding; Form SSA-1042S, Social Security Benefit Statement (Nonresident Aliens); Form RRB-1042S, Payments by the Railroad Retirement Board (Nonresident Aliens); or Form 8288-A, Statement of Withholding on Dispositions by Foreign Persons of U.S. Real Property Interests, that supports changes made on this return.
Attach to the back of Form 1040-X any Form 8805, Foreign Partner's Information Statement of Section 1446 Withholding Tax, that supports changes made on this return.
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