Each series of bonds issued under the authority of this act [21-11-15, 21-11-16, 21- 11-18 to 21-11-26 N.M. Stat. Ann.] shall be designated by the letters “A,” “B” and so forth, to the end that each series shall be kept separate, and all of the requirements of this act shall apply to and shall be faithfully followed, done and carried out as to each of said series.