At each catered event at which alcoholic beverages are served, the holder of a general statewide or limited statewide caterer’s license shall: supply service personnel, including bartenders and waiters; ensure that the service personnel are present at all times during the catered event; have at least one individual at the catered event who has been certified by an alcohol awareness program under § 4–505 of this article; ensure that the sale of food represents at least 70% of the total cost of the catered event; and return all unopened containers of alcoholic beverages to the holder’s principal place of business at the end of the catered event. The holder of a general statewide or limited statewide caterer’s license may not: deliver alcoholic beverages to a catered event without service personnel present on the premises of the catered event; and except when operating under an on–premises retail license that may be annually renewed issued by a local licensing board, serve alcoholic beverages at: the holder’s principal place of business; or an event for which the holder is a sponsor or promoter. To ensure product integrity, a partially used keg of a malt beverage may not be used at another catered event.