They typically do a lottery once a month or so in the first half of the year and then maybe 1 or 2 lotteries the second half. Each lottery will usually contain 3-4 bottles. Last months was the BTAC. Prior to that was the Pappy lottery. The next one coming up is a mix of BT products (EHT BP, Weller SB, Blanton's Straight from the Barrel)
When you go the enter the lottery you basically pick which of the bottles you want to be entered for, so each of the drawings are independant and you can win any or all or none of them. You also have to give your name, address, etc along with picking a home store. When you go to buy the bottle you have to give them your Driver's License and it has to match the address you provided, no exceptions. I'm sure folks will register their wife and kids but outside of that i think it stays pretty fair.