The Mexican flag with "1824" written on it did NOT fly over the Alamo during the 1836 battle.
The defenders of the Alamo flew the flag of the Republic of Texas — a single large five-pointed star on an azure field (the "Burnet Flag," adopted Dec 1836) or possibly the 1824 Mexican tricolor with "1824" in the center as a political statement by federalist Texians supporting the 1824 Constitution against Santa Anna's centralism.
The Alamo flew a Texian revolutionary flag (likely the Lone Star). The "Mexican flag with 1824" is a powerful symbol of the federalist cause — but not historically verified as the Alamo's banner.