This subtitle does not apply to a person who executed a legally binding written contract before July 1, 1973, to sell, fabricate, assemble, glaze, install, consent to, or cause to be installed, glazing material other than safety glazing material in, or for use in, a hazardous location in the State. This subtitle supersedes any county or municipal ordinance that relates to safety glazing, that is less stringent than those in effect under this subtitle. This subtitle does not preclude a political subdivision of the State from adopting and enforcing requirements and regulations that are more stringent than those in effect under this subtitle.