As a suggestion: Each time someone plays a 1 year turn, they then have until the end of the following week to upload their write-up of that game, so that each person who receives a save file will always be in the dark about what has happened for the past in-game year.
You may even make the turns 5 in-game years long or however much of those 5 years can be done in 1 week before posting the save file. This way, the various histories will be even more inscrutable to the person who gets the saved game.
A further modification to this idea might be that at the end of the 1 week or 5 in-game years, that the fortress must be abandoned before saving the game. The next person then will have to start out "recovering" the site, and will get to rediscover all of the stuff that happened there in the last turn with all of the population marrying, having kids and so on during that two (in game) week between Overseers.
One further expansion on this idea is that there are two fortresses in 1x1 adjacent plots, but run by different dwarven civs. Each one takes a turn building for a year or five, trying to outdo their neighbor in a kind of "Keeping up with the Urists" type of contest. They take turns back and forth, attempting to have a more valuable fortress, or to have the highest towers, or to have the most skilled craftsperson/warrior, ect... Anyway, each fortress is retired before the game is saved and the other fortress is then unretired for their turn. If ever the game crashes do to a "nemesis unit" error, then another adjacent site can be embarked on by that civ and the old one is retired for good instead.
All of these could be a lot of fun for a parallel fortress game.