For the most part, once the inventory of studios are all booked, a member will be told everything is booked when they call to reserve. Then you may waitlist or try another resort. On occassion, something may happen that forces an upgrade as people have mentioned. At the other Disney hotels, upgrades are more prevalent. If all Lagoon view rooms at the Poly get booked and people keep calling for Lagoon views, they will normally get a reserved room at that rate. Depending on the check-in activity as people arrive and housekeeping's rate of cleaning checked out rooms, some people may be surprised to learn they've been upgraded to Concierge if all Lagoon view standard rooms are in use. This has happened to us at both Poly and YC on 3 occassions in the past.