I think they explicitly didn't give a number do they could leave things open to change. Like they probably have a number in mind, but if they told us that number they would be bond to it. This way they can do the work they want and if it ever stops being profitable enough or if time and schedules start conflicting, they aren't obligated to push themselves.
It's the smartest move on their part, but yes they did pluralize it, so they are beholden to at least two more after the pass.
I'm optimistic it will be more just because if the pace they are making right now. It seemed like Joker too forever, but since then they have been doing out faster and faster. The trailer promises Terry in November, which gives them the months to get the fifth character it before their initial deadline would be up. I wouldn't be surprised if number fine is out sometime in January.