Bonds issued pursuant to this chapter may be in fully registered form with ownership recorded on books of registry kept for that purpose by or at the direction of the board. The board may also provide for the incurrence of debt through use of a book-entry only system to be maintained by a securities depositary. The bonds may be executed by the manual or facsimile signatures of the officers as may be designated by the board, or the board may provide for such other means of verification of authenticity of the bonds as it may consider appropriate. In the event of any change in officials, bonds executed before the change continue to be valid.