I've been tracking sales at BLT, AKV, and SSR for the last 9 months, and I've noticed some patterns in DVD's use of UYs. When BLT, AKV, and SSR's THV Units were opened for sale, DVD declared at least one Unit for each UY. It makes sense to do this because the initial sales were aimed at existing DVC members, and those members already had all eight UYs. At BLT, February was the default UY until 9/09 or 10/09. But during the Holiday season DVD began pushing February UY again, mainly because it was offering "double" points (2009 & 2010) for those who bought by January 2010.
I've always wondered why DVD picks a certain UY as the predominant UY for a resort. At BLT, its February, at AKV, its December, and at VWL, its August.