If a carrier has five or more tariffs on file with the Commission, an index of such tariffs shall be filed consisting of two sections, the first section listing the kinds of service alphabetically and showing the numbers of the applicable tariffs and the second listing the tariffs numerically. The index shall be supplemented each month in which changes are made in order to bring the information to date, and shall be reissued within a period not to exceed one year.
52 Pa. Code § 23.15