Immediately after making the proclamation, and before separating, the board members of each precinct in which votes have been received by paper ballot shall enclose in an envelope or other container all ballots which have been counted by them, except those endorsed “Rejected as double”, “Defective”, or “Objected to”, and securely seal the envelope. The signatures of all board members of the precinct shall be placed across the seal or the opening of the container so that it cannot be opened without breaking the seal. The precinct election officials shall return all the ballots to the commissioner, who shall carefully preserve them for six months. Ballots from elections for federal offices shall be preserved for twenty-two months. The sealed packages containing voted ballots shall be opened only for an official recount authorized by section 50.48, 50.49, or 50.50, for an election contest held pursuant to chapters 57 through 62, to conduct an audit pursuant to section 50.51, or to destroy the ballots pursuant to section 50.19.