You're talking about national parks, I'm concerned about Army Corps of Engineering areas designated for recreation. There is no way to guarantee access at this point. You have to buy the pass from recreation.gov, then show up, then find out the park is 'full'. I have no idea what this means, there are no published limits, and I am still a valid pass holder.

The website is basically a scam because you can't enter if you don't have a pass. But buying a pass doesn't guarantee access. I can't make a reservation either, I have to get there in line (after buying the pass online) and hope I can get early enough before the park is 'full'. This basically means the park is off limits.