You can’t go by anything they try to tell you, watch the videos, watch them carefully, THEY NEVER SHOW YOU A FULL PAGE.
http://seattlest.com/2008/01/30/obamas_mixed_an.php
1st video answers my question on official version -- One year at Seattle and 2 yrs at Mercer Island school. Three years in Washington total.
1st video - I also have thought it odd that Chip points to his senior photo (assuming it's his senior photo) and not SADO's.
We would have to see a "live" yearbook to know its basic design with respect to how they highlighted each class. For instance, many yearbooks of that era only had group class photos for students in 10th & 11th grade---and individual photos for 12th grade.
1st video --- Susan Blake: "Here's Stanley, 1959 Quill & Scroll."
2nd video - 1:40 min --- another all girls photo
SADO may have had a senior picture taken, but I have never seen any evidence that she actually attended her senior year at Mercer Island. Quite the contrary, and, if anything, I have thought that most interviewees avoid mentioning her senior year.