Ugh. Really? How are they any good at what they do?Also, just fyi, if you have touringplans.com, look at what they predicted vs. what they saw. Many of those Sept 1's & 2's turned out to be more into the 3/4/5 numbers. Which is what early/mid Dec was in 2014. So, if you were ok with those crowds, it should be comparable. The only caveat I will add is *for us* dealing with 3/4/5 crowd levels was easier in Dec cause the heat in Sept made us more irritable. Maybe that would be a non-issue for you.
Ugh. Really? How are they any good at what they do?
I was at WDW 9-10 and 9-11. I think any week that has a holiday in it leads to more people. While moving around in the parks was very manageable, it was extremely HOT & HUMID. The wait times were longer than I expected. We had a 45 minute wait on BTMRR and it was before 10 am!!! The crowd calendars were way off! My DD who complained about it being chilly on our November '14 trip, has decided never again in September....she wants to go when it's much cooler and will gladly wear a coat!
We were in WDW 9/19-9/26. In every online group I was in, everyone talked about "low crowds!!" but when we got there, it was not low crowds. Now, I haven't been in ten years, so it was objective to me, but my mom who goes at least once a year, said it was way busier than normal. Most rides were about 30 minutes and up. In DHS, ToT was 105 minute wait on 9/23. While it wasn't shoulder to shoulder, it seemed pretty busy. When we got back my mom read that the supposed 3 crowds were actually 8. So yeah.
Did it impact our trip much? No. Would I go again in September? No. It was SO hot and humid. I'd rather have cooler temps!
Your comments and so many others on this thread and others have me wondering how many people ended up trying September once (and it just happened to be THIS year) and they are all saying "never again!"
I'm starting to think next year will be a little more normal.

Your comments and so many others on this thread and others have me wondering how many people ended up trying September once (and it just happened to be THIS year) and they are all saying "never again!"
I'm starting to think next year will be a little more normal.
The NOJ (likely) weekend falls during your planned dates - that would make the Friday and Saturday at MK virtually impossible to do. Also, waterparks for those days would be packed. Once the weekend ends, you'd be okay in MK unless the Halloween parties start right away - that may also make MK busy on non-party days and short hours (which start getting packed at 4pm) on party days. Really, I would go when you'd like to go, and ignore when it will be "quiet". I think September MK will be packed next year (since the month has the current bounce back free dining offer, the holidays, the NOJ and parties, AND the likely cheap ticket pricing once surge pricing hits)...although having said that, I think the other 3 parks will be relatively dead...so if they are your goal and not a majority of time in MK, you should be okay.