Posted November 16, 2017

"d) Withdrawal Right: we give you the right to withdraw from a purchase of GOG content without charge and for any reason within 30 days after you bought that GOG content, IF it has not been downloaded, streamed, activated or used in any way before then. If any of those things happen then your withdrawal right is lost."
https://support.gog.com/hc/en-us/articles/212632089-User-Agreement
(Point 6 - Refunds and returns)
Frankly the publisher should really offer a deep discount for existing owners to get the new version, or even give it "for free" if one has the earlier game with DLCs. Similarly like how The Witcher 3 was handled, I got the GOTY version on top of the base game + DLCs I had bought earlier.
I'm glad I never got around to buy PoE, part of the reason was because it had so many different editions and as I learned there is still DLC coming out for it. Similar reason why I haven't got around to buy Age of Wonders 3 either, I hope it gets a "definite edition" as well that I can buy.