This comes from the FAQ they just released today. So, I guess it comes down to, are they going to follow their own rules or not? It sounds like they are making an online acceptability list to reference and put the 11 day element out there as a secondary measure to refer to if you can't see the online list. We will see if these continue to match up, but it looks like the next chapter pack is scheduled for June 21st and will qualify with both sources. Unless there is a delay (that never happens) and then the online sheet might get out of sync.
"For most Relaxed and Formal tier events, a product is legal from
the time of its release until the time of its rotation (if applicable).
For Premier tier events (such as the North American and World
Championships), product becomes legal 11 days after its official
release to ensure that all competitors have sufficient opportunity
to obtain and familiarize themselves with all products in the
defined pool. For a current list of legal product, see the FFG
website, here:
https://www.fantasyflightgames.com/en/op/legality/
2016 North American Championships
For the 2016 North American Championships, the following
product sets will be legal:
✦ A Game of Thrones: The Card Game second edition core set
✦ Wolves of the North deluxe expansion set
✦ Westeros cycle Chapter Pack expansion sets: (Taking the
Black, The Road to Winterfell, The King’s Peace, No Middle
Ground, Calm Over Westeros, True Steel)
✦ War of Five Kings cycle Chapter Pack expansion sets:
(Across the Seven Kingdoms)"