Disney has several types of inventory - its outlined in your purchase documents and by timeshare law - and there are also some GAAP accounting rules at play in terms of inventory and revenue in different divisions of the same company where those divisions keep their own balance sheets. (In other words, it either governed by your contract, by timeshare law, or by the SEC - Disney can't do whatever it wants - either for their benefit or ours). There are rules about how each type of inventory can be used.
All the inventory that is sold and held for points is available to members for points. This is the inventory you log on and book. Once a room is booked for those points, those points are spent. They cannot hold back any of this inventory. This is the vast majority of inventory at any resort out of active sales.
Disney does hold back a small number of points - they use this for maintenance. It really isn't enough for welcome home reservations - it honestly really isn't enough for maintenance - but it is enough to take rooms out of service for the renovation/refresh cycle.
There are points not yet sold or bought back through ROFR and not yet sold. These are Disney's points to do with as they wish. Points have to be declared in order to reach this status. Rooms that are built, but have not yet been declared into the condo association are different - there are no points associated with those rooms at all and they cannot be booked for points. When Disney doesn't have a lot of inventory, there aren't a lot of points in this pool. MOST of this pool Disney wants to sell for cash because that's revenue for them. They aren't holding these back, they just haven't sold them yet.
There are points that members have used, but they are using them outside of DVC resorts. DVC sells those points (as rooms) to CRO to pay for a member's cruise or Disney Collection choice. Or they deposit them with RCI to pay for a member's stay in an Alexandria timeshare. Those points are never available to us as they've already been used, and can be the biggest confusion for new members - because a room sold to CRO shows up on the Disney Hotels system, but cannot be brought back into DVC inventory for you to book. So a lot of members get mad when they see availability for cash, but not for points.
There is what is called breakage inventory. This is what happens when you don't use your points - or all of your points. Every year members will leave some points on the table. At 60(?) days DVC turns unbooked rooms over to CRO to try and monetize them. Members see some of the income (not all) in the form of a dues credit (called "breakage income" IIRC), and some of the income they keep themselves (for administrative overhead and because they get to). This is the inventory that Disney can claw back - the room that you see on the CRO website that when you call member services they put you on hold and go get that room back. Its the minority of rooms available through CRO, but sometimes they are there. Disney can use these for Welcome Home inventory as well.
Note that points and rooms aren't the same thing. But Disney owns enough points to book some rooms - and rent them to CRO or whatever.
I may be off a little here, some of our legal experts or someone who knows the system better can feel free to correct me. But they don't "hold back" any inventory that is bookable to members - i.e. any inventory that is declared, sold, unbooked, and owned by members - that would be a problem with contracts, timeshare law, etc. Last year was really strange in terms of inventory - it was likely unbooked inventory sent over to CRO that they clawed back - since last December there was a whole lot of inventory hitting breakage. And rooms were continually getting cancelled as people hoped that the curve would flatten and then it didn't. In a normal year, there are not CCR studios available in December for anyone on short notice.
