well thinking of it another way, all the Walt Disney World resorts were open the same amount of time in 2020 so their actual cost will have been affected similarly
budgets / dues are future projections / calculations like you mentioned and if there is a surplus, it normally gets moved to the capital improvement fund for each property; since the effective 2020 dues (2020 - credit) reflects actuals (credit given back, not to to capital improvement fund), this is probably the best view into the actual costs of running the DVC resorts we have