Actually, most dates, except some in May and some in October completely fill up in the lottery. But lots of people drop out -- first by not paying for the slots they win, or by not showing up on the date to pick up their paid for permits.
If you are looking at the count of "first choice" people, that really isn't a good thing to trust. People put in lots of alternate dates, so the count gets much higher for your date.
Note that the Lottery Progress Report page states: "This data is from the first choice only. When alternate choices are considered the number of people requesting a date is greatly increased.
" What that means is that the entries processed earliest in the lottery may grab your date. If an entry's first choice is not available, the process then tries the second choice, then the third, until all choices are tried, or one of the choices is successfully satisfied.
However, if you look at our "Unused Permits page
", you can see that for every Thursday in September, there have always been plenty of unused permits available. If you didn't even enter the lottery, you could show up in September on a Tuesday or Wednesday, and always pick up (for free!) a permit for the next day. Unfortunately, most people don't like to gamble on that, so therefore we have lots of permits going unused.
...edit: I just looked back through the past 5 years of Unused Permits numbers, and there is Not One
Thursday where there weren't unused permits available! (Too many negatives in that sentence. It means that on any Thursday, there are always permits available.)