Aloha Dave,
I hope the following isn't too confusing in this newbie section. We only own unconverted traditional weeks. I am not an expert on either RCI Points or Wyndham points.
I am not sure of all the facts related to the OP's problem. One hunch I was trying to confirm or refute was that the ebay listing was for a traditional Pahio (now identified to be KBV) unit that the seller assumed was converted to Wyndham but was not and that the deed for the traditional ownership was processed and of course Wyndham would not know about it. That is a long winded way of aligning with your statement: "My other guess is if you contact Advanced Financial, the title arm of Grand Pacific Resorts, you'll find your deed has been transferred to your name through them, and you now own a Week at KBV."
Given that the OP wanted a Wyndham based resort (a fine idea if bought resale), she should pursue getting the situation corrected unless there is a reason to change her mind. As I previously stated, winding up with a free 2 bedroom KBV oceanfront might be a valid reason. If it is a lagoon view (statistically more likely), those are readily available for $1 so there is no reason to currently accept that if the desire was for Wyndham.
Long ago before Dave Walters (original developer) sold out to Wyndham, his sales crew were heavily promoting conversion to RCI Points rather than staying in traditional weeks exchangeable in RCI's traditional weeks program. Long ago, I was under the impression that the RCI Points feature did not transfer with a sale; however, I am not sure whether that is correct or not. Once Wyndham took over, I imagine they only promoted conversion to their own club Wyndham program which required purchase of at least one new Bali Hai unit and a fee for each traditional Pahio unit to join. Based on long time observation of ebay, I believe that Pahio units converted to Wyndham retain their Wyndham nature upon resale even if VIP benefits do not transfer. If your statement: "sales of converted Weeks revert back to the underlying Weeks ownership" is correct, it is news to me. If a tugger is sure they know, please speak up.
I believe KBV owners who bought into the Wyndham program can withdraw their KBV units from Club Wyndham but do not get any of their money back.
Grand Pacific is the current management company for KBV. Owners of traditional weeks may use Grand Pacific's internal exchange program without annual membership fee (but with a fee for an actual exchange). I am not sure what you meant by "And that means it would fall to Grand Pacific Resorts, the current management company."
Jack