That is somewhat true. Usually the boulder is the last puzzle to be solved but not always.

The correct wording would be that once all techs are researched fully and all 16 puzzles are completed the game is technically done. However, your villagers will continue on in their village unless you delete them so they are fun to watch!
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My VV2 story, "A Twist of Fate"
And don't miss Krystal's stories, all three of them!
"Life is too fast... unless you're in traffic."