Summer courses before matriculating

Hi all! I am an enrolled transfer student for the Fall of 2024, but I was hoping to get a head start and take a summer course. COS advising said to register as a special student, but once I did that the office of the Registrar said I wasn't allowed to register as a special student before matriculating. Does anyone have any experience with this or know about this rule? Seems weird that the University itself isn't consistent with the rule. Thanks!