As you know, the majority of cadets never attended SLE so there is no downside with not being invited. Good news is your son is ready to apply to USMA when the application opens.
By the way, there are other great ways to see the Academy. One good route is by attending one of the USMA summer sports camps. Many of my students have participated in them across all of the SAs. Students stay in the dorms, eat in the mess hall, meet cadets and staff, and they also work with the coaching staff. I hope things go well for your son!