It’s not hard to figure which planet in a system is habitable. And throughout the Star Wars movies, there are numerous instances where they refer to a system with the assumption that the listener knows which planet is being referred to:

“You prefer another target? A military target? Then name the system!”

“It’s only a fragment from a probe droid in the Hoth system, but it’s the best lead we’ve had.”

And, of course, the Dagobah system reference. There are probably more.