Hey Nell! When I wrote my letters I had several that were addressed differently depending on the board I was applying for. Guard and reserve were addressed to NGB/AFRC but also specifically to the unit I was rushing and/or applying towards. My Group CC addressed it to “Air Force Officer Selection Board”. For AD, I’d probably address “UFT Board #xxxx Board” or something similar to that. I didn’t apply AD so I can’t really talk to it, but as a successful Reserve UPT Select that’s what I did when I started applying and rushing squadrons. Here’s a few options, I hope it helps! Good luck!