My understanding is that for all services applications are only boarded once. That being said, one must understand the technical meaning of boarding in this sense. Boarding means the board looks at the application and scores it. It's then placed in a stack of other boarded applications. At the end of the board the top x scored applications are awarded scholarships. The stack is retained for the remaining boards. Additional applications get added at the next board, and the remaining top y (including older applications from previous boards) are awarded a scholarship. Your score can be changed between boards by quantitative measurements (eg improved SAT/ACT scores), but it's never scored by the board again.
So, although an application is "boarded" only once, each board considers the application for a scholarship at the end of the scoring. This is why folks say to submit the best application you possibly can, as early as you can put that application together. If you submit too soon you will perhaps lose some "qualitative" points that you can't get back later, like you can "quantitative" like SAT and ACT.
I may have over-simplified, but that's essentially the process as I understand it. It works as a model in my head anyway.