Yes, as far as I can tell, the game usually considers adventures unsuccessful if you fail the first stage and have to stop the adventure and try again. You get text about the failure, but you're really expected to go back and try again, and then narratively in a lot of cases, it's like you didn't fail the first time at all. (Like in Aaran's adventure, when you fail and then he breaks the fourth wall a bit and talks about how you will have to go through the whole thing again, as though the first attempt had never even happened.)
The problem is that with Carnage On The Fields and Once Discovered, you can fail at the first stage and then continue all the way through the adventure, including getting the final reward (or "reward"), and narratively it makes sense for that result to stand as what actually happened to your character. But failing the first stage still leaves it marked as "unsuccessful" which means you could go back and try again.
The fact that this is possible seems like it might be unavoidable as part of how the engine works. But it's easy to work around, by just not choosing to play through the adventure a second time. My concern is just whether the game will actually remember what you did, if you use that workaround and leave it standing as "I got Diavesque but in a way that left the engine toggled to unsuccessful."