The specifics of how they draw the tags are the most important. Say there is a unit with 30 tags. The same unit has 300,000 total squared bonus points of applicants.
My guess of how they complete the draw is they assign each individual entry (total squared bonus pts) a randomly generated number. The lowest 30 of those 300,000 randomly generated numbers draws a tag. So, each entry has a 30/300,000 chance of a tag (.01%). So, a person has 10 pts. Since each random number is independent (ie RANDOM) you could calculate the chances of being one of the 30 lowest random numbers this way, 1-(.9999)^100 = .0099506% x 100 (10 pts) = .995066% chance. You could just say 100 x (30/300,000) = 1%, close enough. The NR 10% issue (and a single individual having multiple numbers within the top 30), complicates slightly, but from a practical perspective the above will get you close enough. This is pretty easy to figure out for each individual district once you calculate the total entries (squared bonus pts) in play. ****Obviously, you can only look at past draw odds and figure this out, but, the past is the best predictor of the future, so there's that.****
They could operate the draw differently (each tag is drawn independently of one another) but I think that is unlikely because the above is really simple for them to run (and probably more importantly pretty difficult to screw up).
Flame away.