Back then, they mostly just sang the songs according to what they thought they heard....wasn't too much 'research' going on.
Why, even Mudcat had to be typed out on an old typewriter and corrected with white-out. Sometimes it took weeks for a page to be carried down to the post office and mailed to the next member for comment! ...and 'guests' would lay traps and hijack the mail and alter the words. Maybe that's where 'eyes' instead of 'Iris' got in?