You can check mousesavers.com for "historical data" on discounts for the past five years. They are listed by time periods.
But I don't think you will see the same discounts that you have seen the last three years.
With Disney reporting the parks are way up in revenue, I think they are going to start weaning us off discounts. I would expect there to be free dining for the usual August/September and some scattered here and there.
But I would suspect around holidays, like in November, they are getting more successful filling rooms and you won't see it next year.