The War Story narrative rules from Nordic Weasel has seen a small update.
The new version adds an additional chapter "Setting Odds" with a mechanical system for figuring out the odds of a given attack, including some options to introduce random factors into the system.
It's basically an outgrowth of how we tended to resolve odds-setting in the first place, so feels proper to include it.
It IS optional, so if you already have a method in place, just stick with that.
No other changes were made, so you can just print the two new pages.
If you aren't familiar with War Story yet, it's NWG's "narrative wargame", featuring a more conversational "matrix-like" approach to gaming.