It took me a while to notice that creating a new game on an old installation is not the same thing as creating one immediately after install.
I have a template save where I added cold/hot weather clothing to all my townies' wardrobes (instead of letting the game choose it randomly). Every time I start a new game I load the template and save a copy with a different name. But recently I wanted to start a completely fresh game and was surprised that all townies had kept their assigned pieces of clothing. Also all the households I had added to my world were still present.
The only way I could think of to produce an out-of-the-box game was to temporarily rename the Sims 4 folder in my settings directory (maybe moving the game saves would have been sufficient, I didn't bother wasting time to find out).
So, every time I load an old game the next "new" game uses the last loaded world.
Am I the only one having this problem or is that common on everybodys installation? And if so, is it a bug or intentional? Is the world and it's households a static thing?