You are correct about the membership rule. If I remember correctly, corps had to declare either 100% (all members were veterans) or 80/20 (80% of your membership were veterans).
Reilly, Archie, and Skyliners (they were called Garbarina then) Officers met and decided they would declare 80/20 and would not protest each other. Those same Officers were shocked when they were notified, after the prelims, that they had been protested. There was much finger pointing between the three corps. There was even a fight when one of the Officers threw a punch at another Officer. That Officer ducked and the culprit hit the wife! Years later it was discovered that the protestor was Jim Costello of Hawthorne.
Ah, the stories