Assuming that the BB in October will be a room discount for the following year (my guess is it will be but that's just a guess), then there will almost definitely be blackout dates and will almost definitely have room categories that are not included in the BB or have already sold out for the number of rooms that were included in the BB pool of rooms.
Discount percentage can vary from year to year. If I had to guess I'd say that next years will be no more than 5% less than what they offered this year. I don't know what this year's room only BB was. I'm sure it's somewhere on this board.