|Maps like this...|
As a result I've amassed material in different notebooks: one central book for all campaigns and several smaller binders for individual groups. Because I know much of it is going to end up in Wandering Heroes of Ogre Gate books, I tend to prepare very carefully and with an eye toward having it all organized toward that end. That means I write most things out the way I write them for publication and make my maps knowing I will need to hand them to an artist at some point. That allows me to playtest the material as thoroughly as possible. It also means that me and my players have seen the system itself in action over a long period of time.
|...become maps like this...|
There are different ways to playtest. One is the individual, focused playtest (where you test out specific mechanics, scenarios, etc). These are good when you are putting stuff together or when you need to test specific rules. But they don't give you as much information as a full length campaign. Things come up differently when there is more context, history and the stakes are higher. That is why I find more value in running systems over the course of longer campaigns during and after development.
You still won't have perfection that way. Even with focused and campaign playtests, you can miss things or not see certain problems and potential combinations clearly. But you get a much better sense of how the game plays and where it needs to be improved. You also are more apt to see where ideas that look great on paper or in theory, just don't pan out (this is why my Grudge Rules went through about four iterations before they reached the final state).
As an example, in Wandering Heroes of Ogre Gate we had techniques that felt too powerful in focused scenarios so they were flagged. However we found that in a full length campaign their utility was often more situation-dependent. More importantly we learned that it was actually a good thing to have some techniques that are a bit more powerful than the others in a wuxia setting. If you think about the old martial arts movies, a standard plot line is a big villain has some great technique that others can't defeat, so the heroes have to invent a counter to match it. You also see scenarios where the hero relies on a particular Kung Fu Technique but meets someone who comes up with the perfect counter. For that to work, there have to be some rough edges, where certain techniques stand above the others. But you also need there to be room for players and GMs to respond and create new techniques. This is exactly what we did, allowing for a world of evolving martial talent. But the game wouldn't have developed this way had we not been doing regular, ongoing campaigns.
The rulebook for Wandering Heroes of Ogre Gate should be available very soon. After that, people can expect a full adventure module, several free or pay-what-you-want setting supplements and an expansion called Profound Masters of Ogre Gate (to help with higher level play). These will all be developed using the process described above (and a couple of them have been completed).