The following is my personal opinion since I don't sit on the selection committee. The committees are tasked with selecting the best candidates while meeting certain objectives. I would suspect this is true with most schools. The military strives to have their officer corps representative of their enlisted corps. Maybe sometimes they take someone with a WCS that is lower to achieve this objective. I would also argue that a lower WCS doesn't mean you are less qualified or you will be less of an officer. WCS is a way to apply some form of comparison/standard. I would suspect there is a certain minimum WCS they will accept. Not sure how much, if any, subjectivity can be applied to WCS. In the end, the goal of admissions is to select candidates that can be successful in completing the program and ensure a top quality supply of officers to the fleet. One thing I always thought was special about the academies was their diversity (geographical, ethnic, income, etc.). SA's have candidates from every corner of America. You will find this diversity will enrich your educational experience by opening your mind to other life experiences and beliefs. I believe it is why our military is one of the most adaptive and responsive in the world.
So think big picture. Each year, the SA has a certain number of appointments to fill. They do this through Congressional, Presidential, Sec Navy, etc. Candidates with multiple nominations give the SA flexibility in how they slot appointments. The SA will pick a candidate from slate (assuming one is qualified) and "charge" that account. The others on the slate (up to nine) get thrown into the "fish bowl (my term)" where they compete nationally with all the other "leftovers" from around the country. If you think about that and remember what I said above about GA it will start to click. Theoretically, you could have 20 receive appointments in a state just from the two Senators' slates (two that get charged direct to the Senators and 18 that get SECNAV (fish bowl)). When my DD went through the application process, she had two nominations (Senator and Congressman). On both slates were individuals with LOA's (that will make one nervous). While she had extremely high stats, she did not have an LOA. Having an LOA may not mean you have a higher WCS either. To this day, we do not know how she was appointed (charged). She received her appointment early December. My DS had two nominations (Senator and Congressman) and no LOA. He did not go to summer seminar. He received his appointment in March. I throw this out because many get caught up having an LOA's and/or having attended summer seminar. There are many more factors than LOA and SS attendance.
All this is a long winded and a rambling way to answer your question. I've seen stats in the past that would indicated once you are triple qualified and have a NOM, your odds are generally 50-50. If your WCS is strong you likely will prevail in the end. How you prevail is affected by many factors and circumstances. It is not always clean cut. Each State has its own personality. How the candidates are nominated (competitive, principle) and when slates are submitted can vary. All impact timelines. So be patience and good luck. Continue to work all avenues for commissioning (NROTC) because strange things can happen.