If it's important that some things have happened in their past that will play forward into the adventure - you know, like how exactly they died - well, that's what adventure moves are for. They were called "love letters" in the original Apocalypse World, and honestly I like that name a bit better, but you can read up on them in the Advanced DelvingAdvanced Delving chapter. They differ from other player-facing moves in that they don't have to flow out of a player's narration of what their character is doing; in fact, they're notthey don't have to be freely available to the players at all. They reflect a unique circumstance, assume some narration, and influence how events play out over a longer period of time.
The adventure moves are still how you'd make the transition to the new form of your campaign, because otherwise you'd be walking into a scene where your players could theoretically act freely with a plan for how it's going to end, and they'rewe've already established that's a bad thing. Adventure moves that you deploy in this way are at once easier and harder to write than they might be for a campaign setup. Easier because you've been playing in this world for a while and you know what kinds of things your players care about that you can place in the crosshairs of a "how you died" move. Harder because the adventure moves are part of the sell and you need to be more open to negotiation with your players about what's ultimately at stake.