There aren't necessarily rounds of LOA's being issued.....if the academy thinks a candidate is deserving of a LOA, they send one out. Your chances are 50/50 just like everyone else who applies. I wouldn't associate your former squad members LOA with attending SLE. There is a very high percentage of people who attended SLE that will be denied admissions. Just keep working hard and let the chips fall. There are too many things that you can't predict in this process so control the things you can control.
The application period is a marathon not a sprint. The best advice is to worry about the things you can control. You should be getting in the swing of your senior year by now and working to complete your application. Now is the time to finish the nomination applications as they usually take more time than the actual academy process.
An LOA can be given at any time in the application process.
For USMA, do not concern yourself with LOA's. They are not used at USMA in the same fashion as other SA's. Other than recruited athletes, they are generally only given to a very small number of candidates. It is not a centralized process - each RC decides based on the situation in their region.