"An enrolled bill or resolution is the form of a measure finally agreed to by both chambers of Congress. Enrollment occurs in the chamber where the measure originated and is carried out by enrolling clerks under the supervision of the Clerk of the House of Representatives and Secretary of the Senate. Enrolled bills and joint resolutions are signed by the presiding officers of each chamber (or their designees) and are presented to the President by the House Clerk or Secretary of the Senate, depending on the chamber of origination. In instances in which Congress determines that the enrolled measure does not reflect congressional intent, it can require that changes be made by adopting a concurrent resolution directing the House Clerk or Secretary of the Senate to do so. If the enrolled measure has already been presented to the President--but not yet enacted or vetoed--the concurrent resolution can request its return to allow specified corrections to be made. If Congress wishes to alter an enacted measure, new legislation must be enacted to do so. In rare instances, the constitutionality of certain measures has been challenged based on allegations that the enrolled (and therefore, enacted) text did not accurately reflect congressional action. In considering these cases, the federal courts have typically relied on precedent to refuse review of the enrollment process (or other pre-enactment congressional procedures). This report will be updated as circumstances warrant."
CRS Report for Congress, RL34480
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html