OK. So I stand corrected! Mea Culpa!
I tried to make reservations today for several locations. On one of them, I finally got an indication that the window for reservations for the date I wanted -- exactly 180 days from 11.18.18 -- would not open until 11.19.18!
None of the others gave me any indication, but I did note that, for the weekend of 05.17.19, which is a Friday, the SEASON does not open until 05.19.19. Later openings this coming year than for 2018.
So...For Memorial Day weekend, it looks like, even though the window is November 25th for reservations, it may actually be the 26th instead. Here's your dice...now give them a roll...:S