Hi Dana!
Thanks for your question. You are correct in that there are certain times of the year where a
Disney theme park may reach crowd capacity. Just imagine how many Disney guests want to be at the "Happiest Place on Earth" to the point where the theme park can't take any more guests. That's a lot of people right? It just shows us how much
Disney is the #1 vacation destination for so many wonderful guests throughout the world! :-)
So there was only one time I was in a park where the park reached actual capacity. My family and I were at
Magic Kingdom on Christmas Day, and believe it or not, it did reach max capacity! We were already in the theme park at the time, so we were fine (if you're already in the park when it reaches capacity, they won't ask you to leave). However, we were planning to meet up with some friends later in the day, but they were denied entry due to max capacity. They were kindly asked to consider visiting the other theme parks, such as Hollywood Studios, Epcot, or Animal Kingdom. The good news is these mutual friends had the
Park Hopper Option, so they did go to Epcot (which wasn't at max capacity at the time), and then fortunately, later in the day (closer to the evening), congestion lowered at Magic Kingdom and we were able to re-connect in Magic Kingdom and enjoy ourselves!
So even if parks close at max capacity, it is possible that same park will re-open later in the day if the foot traffic dies down some. I'm not privy to what percentage of the crowd has to leave before they re-open, but I'm certain it has to be a significant number. In other words, if 10 guests were to leave, it's doubtful they would let 10 guests in the park as the other 10 leave.
Also, Christmas Eve, Christmas Day, New Year's Eve, and New Year's Day are the 4 days I'm aware of that have the greatest potential of reaching max capacity, particularly at Magic Kingdom.
Hopefully when you visit, you can enjoy all the parks uninhibited. Have a magical day!
Terry