In Lauderdale County, all persons serving as supernumerary tax collectors and supernumerary tax assessors as of September 25, 1986, shall receive a minimum annual salary payable in equal monthly installments from the county in the amount of fifteen thousand five hundred dollars ($15,500). Any supernumerary official who is paid less than the minimum annual salary shall hereby be paid in monthly installments additional amounts from the county as will provide a minimum annual salary of fifteen thousand five hundred dollars ($15,500). The additional sum shall be deducted on a pro rata millage basis from the county and all subdivisions and agencies thereto with the exception of municipalities to which the person collecting ad valorem taxes is charged with the distribution of ad valorem taxes collected as provided by law.