Dumb question on the 3 Acts

Tagging as act 3 spoilers but this post goes into the rest of the game as well.

So I'm wrapping up my patch 8 playthrough (first time on Tactician, 3rd playthrough overall), and it just occurred to me, I'm not sure where each act begins and ends. Does act 1 end when you win the goblins vs druids war for your chosen side? Are the grymforge and creche in act 1 or 2? The first time I played, I actually took the grymforge all the way into the shadow cursed lands and looped back to the creche after having gone well into Act 2. I didn't even go through that mountain pass portal near Voss because it gave me a worrisome "resolve your unfinished business" message and I didn't want to miss anything. Didn't even know that it was connected to the creche until after completing the creche itself and explored my way all the way back into the Act 1 map. So I'm a little unsure where one ends and the other begins because it's all so fluid.

Act 3 is a little less vague since, unlike Act 2, you lose the ability to travel back into previous acts, but I still wonder where the actual demarcation is. I would want to say it's when you finish Ketheric off as that makes the most sense, but you also get an "unfinished business" message before entering the Shadowfell, and then you've permanently lost access to Act 1. And then the Orpheus reveal, not sure if thats an epilogue of Act 2 or a prologue of Act 3.