Families and kids who show up on R-Day hoping for a spot are misinformed. One cadet candidate who drops on R-Day or later does not equal one open spot. Candidates are notified through official channels prior to and perhaps right up to R-Day, but the academy accounts for attrition and will fill gaps by adjusting the next incoming class, not on R-Day. This is why people who lament that R-Day/Beast/Plebe-year drops deprived some other kid of a spot do not understand the process--the drop rate is built into the number of appointments offered for each incoming class. As it was explained to us, USMA plans to commission about 1,000 officers each year (or whatever the adjusted number is to meet the Army's needs). The number of appointments offered each year accounts for an expected number of turn-downs, the graduating size of previous recent classes, and an expected number of attritions for that class right up to graduation. That's why the incoming class of 2019 was 1257, the class of 2020 was 1300+, and so on.
The number of appointments each year is a function of previously determined yield management and does not account for hopefuls sitting at McDonald's.