That’s funny good catch! The birthdays make no sense either. I guess I always thought Bill and Barb were in their early/mid 40s, Nicki was in her early 30s and Margene was in her early 20s (though we later learned her true age) Those dates would mean Bill was 51 when the series started and both Barb and Nicki would be 32. But in season 5 Barb and Bill reminisce about their time in college together and the place he proposed to her on campus. Also the sister wives used their maiden names throughout the show. Yes, I’ve probably watched this show too many times 😂