Errors on tax forms should always be corrected as soon as possible, in part because the error could affect the recipient’s tax return. There are also penalties for filing a 1099 form that includes an incorrect TIN, which is one error that should be corrected immediately. The IRS doesn’t set a specific deadline for correcting tax forms, but an amended tax return (Form 1040-X) must be filed within three years after the date of filing of the original return or within two years after the date the tax was paid.