Fixed week would mean less available for point reservations for the applicable fixed week. Although DVD has set a limit for fixed week purchases in any particular time period, I am guessing you are going to see more fixed week purchases in latter part of November to early Jan than other times of year.
DVD does not own particular rooms. It retains 2% of the resort and that means 2% of every unit in the resort (a unit is often a combination of two or more rooms). It also gets reservation time via trade-outs by members, through ownership of more than that 2% until the resort sells out and after the resort sells out via getting points back via foreclosures or exercising ROFR. Its use of that reservation time, which could be any time of year and for any size room or view, will also reduce rooms available to members via points. I have suspicions that DVD has done some predatory reserving in the past with its retained points. That suspicion was raised when I found that at exactly 11 months out from the Sunday before Thanksgiving 2013, there were no Jambo GVs available for Thanksgiving night or the night before but the Sunday, Monday and Tuesday night were open -- that seemed an impossiblity if everyone including DVD were following the 11 month reservation window because there is no way a member could have filled the Wednesday and Thursday night without also having reserved and filled the Sunday, Monday and Tuesday night of that week if reserving exactly 11 months out from the Sunday. I sent an email to MS requesting an explanation and it never responded.