I'm not sure Harriett. I've been trying to book a weekend in December and one minute it shows no availability and I go in a few minutes later and there are discount rooms available.
Just keep playing with the dates. I was waiting for my CC to roll over before booking Xmas 2018/2019 and when I tried it came up with some dates not available. Got pissed off at myself for waiting too long, but as I played with the dates, I finally got all the days I had originally wanted. Phew!
I finally got through and got a site for Labor Day week! Now to have a full or higher open up for the week after Thanksgiving this year.....we have a tent site which will still work for our small trailer, but we really want a site with sewer hookup this time.