As outlined in the newly minted document, devs that offer a season pass are essentially promising future content. During the launch process, the dev will be asked.
Bottom line: Valve has published Steam season pass guidelines in an effort to better protect gamers from deception. Because the company views them in a similar light as pre-purchases, they share many of the same restrictions and considerations.
As outlined in the newly minted document, devs that offer a season pass are essentially promising future content. During the launch process, the dev will be asked to commit to a launch window for each piece of content in the season pass.
Season passes should include expected release dates for each piece of DLC down to the quarter and year, and must include at least one piece of content when the pass launches.