BLUF: statistics lie and this process is much too complex to draw anything but generalities from the available information. Control what you can.
All fully qualified (3Q) with a nomination go on a wait list. Call it national if you want, but it's not like other colleges where there is a rank order because of the different nominating sources. Not as many candidates reach fully qualified as you would think. Many MOC will give nominations to candidates that have not opened a file (preferred another SA but didn't make the cut or are just ignorant to the actual process), or that they know have no chance of being qualified but they either don't have enough other qualified candidates or they want to grease the squeaky wheel. Some won't finish, and some won't qualify academically. Concurrently, the RCs are looking at who has a legitimate chance at winning a district/vacancy and are only requesting medical waivers for the most likely. So even some candidates that could become 3Q won't because they won't receive consideration for a medical waiver (whole other discussion, but it is a triage issue to cope with limited assets). This is how you really neck down from the 4400 or so that receive nominations to the 2500ish that are fully qualified.
Each nomination source is it's own competition. Yes, a MOC can nominate 10, but many of the service connected nominations are unlimited so it creates different competition levels. For instance, there are 100 presidential vacancies each year (sons and daughters of career military), and there are usually 7-800 nominations against those. On the surface, it looks like better odds than a district, but it is a national competition. The top end is full of talent, often with candidates that have known this is what they wanted to do for college before they left elementary school and have built the file to support it. The key is to get every nomination you can to better your chances in each of those mini-competitions for an appointment before trying to compete nationally.
The easiest way to think about the Qualified Alternates (correct term for the top 150 off of the wait list) is that they select them after all the nominations are filled. That's a simplification as some will be offered before all vacancies are filled as they are clearly top candidates often outperforming most district winners. Admissions must also maintain a 3-1 MOC-Service Connected ratio for QA and Alternate Appointee selections. The Alternate Appointees come off the wait list as well but aren't necessarily at the top (USMAPS that aren't Soldiers, recruited athletes, etc) and can end up counting for several hundred spots in a class.
With all the nominating sources and alternates, and you CAN end up with multiple appointees from one district. For an average class of 1250, each of the 435 districts can expect 2.8 candidates on average. Statistics lie. Some districts might use two vacancies, smaller states are more likely to have candidates picked up by a senator, some places will have many come off the national list and or service connected nominations. Anywhere from 0 to 20 something (for like a VA-10 pentagon area district) come in from each district.
Basing chances on anecdotal information (n=1) is not reliable either. In the end, speculation on chances based on broad percentages has no impact on your actual chances. You'll never see behind the curtain to know where you actually are on the wait list. Control what you can -
1) apply for every nominating source available
2) finish your application early
3) keep updating your application all the way through the file completion deadline even if you are already qualified
4) reply quickly and thoroughly to any request from your RC, FFR, MOC, etc
5) follow any specific instructions that they give you
6) have a plan B
