Just because this has been sitting a while unanswered, I'll give my impression based on how the resort appears and operates in RCI. With the bump up, maybe someone knowledgeable in II can confirm/deny.
In RCI you see Vistana Resort as two entries as well; 0450 and V450. The 0450 is the "regular" Vistana Resort, and V450 (used to) refer to the Fountains section. They were created separately because they had considerable differences in their ownership and trading rights when Fountains was first developed. That distinction has muddied a lot over time as people upgraded units into the newer programs and resales bumped down to the older programs; by now it really is not indicative of anything. Both seem to get villas in any section of the resort, but probably still better odds of getting Fountains with a V450 reservation, but lots of 0450 reservations get Fountains as well. The one distinction in RCI is that V450 only lists 2BR 8/6 Villas, so 1BR villas can only be reserved through 0450, and V450 should prevent you from getting Courts (lower) or Falls villas that only sleep 6/6.
Again this is RCI specific information gleaned from prior posts and some personal experience, but my impression based on older posts here is that it is a similar situation in II.