It's kind of up to you and your own judgement.
Completed creations can be updated, there's no issue about it, especially if there's bug reports, or feedback that makes you change your mind and enhance features and/or content. But the moment you put your game in that forum, you consider you could widely publish your game and it is "releasable" quality.
Works on progress is if you judge despite being playable you wouldn't consider publishing your game just yet and are looking for some feedback/ideas/whatever the community can send back your way.
From there on, it's your call and what fits best the current state of your game.
Playable doesn't necessary means finished. But finished doesn't mean it can't be updated/improved in the long run.