I would say that Glenn did not add the Citadel’s flag in his book because it has no CW history. Also known as “Big Red” or “Turkey Red”, the red Citadel was a PC replacement for the Confederate Battle Flag. The picture in the Citadel that shows the South Carolina forces on Morris Island in Charleston harbor firing on the “Star of the West” is not historically correct on the artist interpretation of the “Red Palmetto Flag”.
What Lt. Charles R. Woods, commander of the U.S. Army detachment on board the “Star of the West” probably saw the flag that contemporary publications ( The flag appeared as far afield as New Haven, Connecticut, New Haven Daily News, 1/21/1861 ) called “The Sovereignity Flag of South Carolina” . The flag was pictured and described as having 15 white stars on a marine blue ground cross, the center star the larger one; a white palmetto tree and crescent on the upper right hand corner, and the corner spaces, including the ground on which the palmetto and crescent are placed, of red. Similar to the flag drawing in Glenn’s book, page 19.
The “Red Palmetto” flag in the Iowa collection may have SC roots but I don’t think so. There are several other “Palmetto” pattern flags that have ties out side of SC. They may have been made in honor of SC stand on secession, a guess.