There's evidence that the events of the first game have indeed happened, including "spoilers"
I was checking the Wiki for the Ancient Adversary, and whenever his attack, Dreadful Recollection hits, the heroes can do one of these barks:
- N-no! I don't want to remember!
- T-the flesh ...is fluid...it can be...remade...?!
- The gateless gate - n-no!
- L-life...feeds on life...
- A manor...and madness below it!
- I...see pillars of stone...blood and flesh!
- I can't - not again!
I don't know if these barks are limited only for heroes who were in the first game(they probably aren't, which is fine) or if quotes about remembering it can only be said by them, but I think this is evidence that the time loop has been broken, most likely when the protegé imprinted his mind onto reality, which also made everyone forget about the world before the spreading stain.
I know this isn't the first evidence for this that's been found in DD2, but I just think it's a neat way to reconcile the nature of both games' stories without excluding one from the other. I think the heroes minds, after forgetting the Darkest Dungeon, refuses to remember it to save their sanity, even if they've remembered their lives through the Shrines.