As to the setting of all of January as adventure season, that began with OKW when it began in 1991 and has never been changed. At that time the vast majority of holiday breaks for grade to high schools started just before Christmas (usually Dec 23 was the last day if that was a weekday) and returned the day after Jan 1 when it was a Mon, Tues or Wed, on Mon if it was a Thur, Fri or Sat,and on Tuesday if was a Sun. I can remember in the 1990s and early 2000's going to WDW Jan 1 to 8 and parks actually went to having low crowds by Jan 3. It is fairly more recent phenomenon for more and more of those schools to go to longer break periods that include much of the first week of Jan with the result that though crowds do decrease quite a bit from Christmas week size starting about Jan 3 or 4, they still stay quite heavy the entire first week.