Many thanks to the Gentleman who emailed in:

The entry for Iowa is outdated or incorrect. Saps are classed as dangerous weapons. However, it is only illegal to carry a dangerous weapon if it is used in the commission of a crime.
See Iowa code 708.4 willful injury, and several sections of 724 weapons: (724.4, 724.4c, 724.4d, 724.5, 724.8)

If you see something incorrect in the main post please do reach out!