I just went into VIPS and clicked on "Advance Volunteer Request (AVA)"

Here is what came up:

AVA is Not Available for your seat

I agree with your interpretation though - AVA "should be" available from Thanksgiving to 31 Dec.

But, if the company locks you out from even putting in a request........???

In ANC last year, Nov and Dec were both voluntary vacation cancellations and AVA was available - (I'm pretty sure, don't quote me on that, and I don't know about other than ANC)