It’s less of a prose or plot style, and more how the mechanics work. The 2016 ones have been updated a bit but not hugely changed in general - mostly it’s that there are more detailed/varied examples. In the most recent document I have access to, which was from 2022, the highlights are:
- Players must be able to play as male, female, or nonbinary, and games should have an equally fulfilling story regardless of gender, race, orientation etc of the player character (this does not mean that discrimination cannot be written about, but a female PC shouldn’t be excluded from participating in any way in a war, for example, by virtue of gender)
- Games shouldn’t endorse real-world bigotry (this doesn’t mean it can’t be included, but if it is, it should be explored thoughtfully)
- Romance is not mandatory but is an encouraged element; ROs should have other functions on top of being a romance; if romanceable characters have set orientations and/or genders, there should be at least one character able to be romanced by a PC regardless of the PC’s gender/orientation
- There should be a variety of goals to pursue, varied paths through the game, and lots of different states in which the PC ends up at when completing the game, and all the endings should be dramatic and satisfying (even if they’re tragic or bittersweet)
- Choice options shouldn’t be obviously better or worse (“do you want £1000 or a sandwich?”), should be reasonably informed (“go right/go left” when left puts you in a crocodile pit without any clues before hand), and should affect stats, lead to interesting flavour, and/or lead to a markedly different result.
- Failure should still enable the plot to move forward
- Use skills or personality stats, whether opposed or 1-100, to enable players to build their character mechanically (in Royal Affairs these are the Eloquent/Authoritative/etc and Planner-Improviser etc). No one stat should be more powerful or easy to increase than the rest, and they should be widely applicable to resolve problems. These are internal aspects of the PC.
- Use secondary stats to represent the environment, narrative goals, reputations, problems to avoid etc. In Creme de la Creme these are Virtue, Grades, etc. These are external to the PC and go up or down based on choices that test skills. In Creme, you can use high Wit to make a cutting remark and increase Popularity. Popularity can be used later in the game to leverage people to listen to you in a fraught situation.
There is a bunch of other stuff about different kinds of choice structure and game balance, but those are the headlines. In general, it’s about how successes and failures are determined, and providing enough branching that players can have varied experiences through the game.