Some owners trade for HHonors points. That does not take inventory. Also, Hilton tends to bulk deposit into RCI, so they already deposited units to dover the RCI requests.
Seth, when an owner trades for HHonors points, they give up their week to Hilton. That takes a week out of circulation, just as if they'd used their week at an HGVC resort..So it's taking a week out of inventory. Not the same as an owner letting a week go unused and go to waste..
The second part of your answer brings up another question...what if fewer owners request RCI trades than HGVC anticipates when they bulk deposit and HGVC deposits too many weeks with RCI? Do they get the excess back (either this year or next year)?
Seems as though all this wheeling & dealing that HGVC does with trading for points, bulk spacebanking, rescue points, borrow points, bank points, has the ability to bite them in the ass at some point if they don't keep a real close watch on what they're doing. Some owners in the last half of the year have the potential of calling HGVC and getting "whoops, sorry, there are no more weeks to reserve at an HGVC resort this year. You can roll your points over to next year if you like, or take an RCI exchange, but you won't be staying at an HGVC resort unless you trade into one through RCI"
It seems very similar to airline overbooking, and at some point, your calculations are off and you have too many seats booked on a flight...What then?