They mention that change in an old World Atlas of Golf book I have... what else is interesting is that #13, #15, #17, and #18 were all par-fives at that time (mid-70s). Odder still, #6 is a par-four (apparently this was a par-five at one point), so the course then would have had no par-fives at all until you get to 13, and then four!
Has to be one of the quirkiest things I've ever seen from a championship golf course.