No, do not mail the "forgotten" copies with a note, nor should you amend a tax return. Only forms with the federal withholding are required to be mailed to the IRS. If your forms have no withholding, nothing needs to be done. If the forms do have tax withheld listed, please wait for the IRS - they may send you a notice requiring more information about the forms. Once you send the forms with the copy of the notice, the forms won't get "lost" at the processing center and the return will be processed quicker.
