Many cruise lines with fleets larger than 2

will automatically upgrade return cruisers.
DCL does not. And it really does not happen as much as people here believe it does.
Warning: boring math / statistics about to happen
There are about 2625 rooms available per week or 136,500 rooms available per year. If 3% of the rooms get upgraded per week that's 79 rooms. If there are 33 DIS Board families/rooms on each sailing that is 99 rooms per week which is about 3.8% of the total rooms. So if we (DIS) get 3.8% of the upgrades then
we should have about 3 rooms upgraded per week. Do we have that many people reporting upgrades? How many DIS rooms do we have per sailing?
The variables: % of rooms upgraded & number of DIS rooms. I assume that the upgrades are distributed evenly between DIS people and non DIS people.
For one Sailing (not week):
875 rooms * % of rooms upgraded * % of DIS rooms to 875 rooms
875 * .03 * 33/875 = .99 (or about 1 room per sailing)
End of the boring math stuff
As far as who gets upgraded and to where only Mickey & Tinkerbell know for sure (Mickey watches who Tink sprinkles with pixie dust and that family get the Magical or Wonderful upgrade

)