When it isn't just Bugfixes and it get's new content then yes, for me that's not a completed game.
Same with Mario Kart 8 Deluxe. It was completed but then Nintendo decide to make more DLCs. So for me, all the DLCs must be released. Just when Nintendo stop it and don't touch this game with their "new" tracks , just then I consider it as completed once more. As long as there will be still worked on, it's a ongoing game for me.
It doesn't matter if Team Mity, just Marty or just cbob works on this game. As long as either one of the developer still works on this game, it's not completed for me. A completed game for me anyway is a game that get's nothing new in terms of content and just get Bug fixes at most. As long as Marty keeps working on new or altered scenes, the game is not completed for me, it's a ongoing game.