Here are the rules from the Department of State's Foreign Affairs Manual:
9 FAM 42.65 N3 Validity of Supporting Documents and Application Form OF-230
Supporting documents that are subject to change are valid for one year.
This time limitation applies to Form OF-230, Parts I and II (Application for Immigrant Visa and Alien Registration), medical examinations and police certificates from any country visited or inhabited subsequent to the previous clearances. It does not apply to a birth certificate or a third country clearance or police certificates from an area to which the alien has not returned since its issuance. The affidavit of support must be submitted within six months of its signature by the supporting relative, however, it remains valid indefinitely. However, because the affidavit of support is based on the Federal Poverty Guidelines in effect at the time of the visa issuance, it may need to be updated.
9 FAM 42.65 N1 Basic Document Requirements
INA 222(b) requires that an applicant applying for an immigrant visa submit the following documentation, if available:
(1) A valid unexpired passport or other suitable travel document;
(2) A copy of the police certificate for the country of nationality and country of the alien's residence at the time of visa application in which the applicant has resided for six months or more;
(3) A copy of police certificates for any other country in which the applicant has resided for one year or more;
(4) Certified copies of prison records, if applicable;
(5) Certified copies of military records; if applicable;
(6) A certified copy of the birth record;
(7) Other documents establishing relationship to spouse or children, if applicable; and
(8) Records or documents pertinent to the applicant's identity or visa classification with respect to visa eligibility.