Interesting question for the future, but this is not automatically done through Steam?
For example Steam knows that you have base Ashes, at what date and price you bought it, and applies automatically the 50% discount. Free DLCs to come require other registration steps to make?
And, just to make it clear, all the people who bought ashes, at full price, before escalation launch, founders or not, are eligible to receive all escalation DLCs for free till the end of 2017? I think that's what i understood.
