I will say this - they have maximum number that they will sell for a Halloween party. No one knows exactly what that number is, but I don't believe that this would cause them to go over that number. If the event was "sold out" due to people wanting to move, they would just tell those people they can't pick that date.
Now if you bought tickets to the September 12th event because you thought it would be low crowds, and now it doesn't have low crowds, well I don't think Disney will give you much sympathy for a refund. And rightly so I might add. While you can certainly buy tickets to a certain event using that as a guideline, there's no guaranteeing when you bought the tickets it would be low crowds. Now if you called Disney and said, "I need to move to a different nights because Irma did such and such to my plans" then it's quite possible they would be kind and accommodate you, but they certainly wouldn't for the other reason.
You're sorta right...
And the following is actual experience combined with educated conjecture:
The max occupancy of mk is about 100,000 if I remember correctly...
The Halloween max is probalby in the 30,000-40,000 range. (Which I'm think is a moderate-high average daily rate, but condensed into half the hours of the day)
The old Eride...the last true limited ticket event (they are "hard ticket events" now...which is a definite difference) was 12,000-18,000 or so (can't remember exaclty)
So say the cap for Tuesday sales is 30,000?
Does that mean they not let in 10,000 overflow? Absolutely not
Will you know the difference? Maybe...but can't prove it.
Will they tell you nobody above what they promised is in? Yes.
Is that honest? No way, hurricane Jose!
I will say this: after Disneyland last year (which Jade tried to make a sly point out of but pooched it and fell)...I have little doubt their daily max is the exact same as the Halloween max...it was awful.
The space of mk at least mitigates that a little.