It's usually last for me also. But in a current game, I wanted to see if I could complete the gong before getting L3 Farming. I managed to do it with only 11 villagers! By that point, I also completed the shells and 11/12 of the butterflies, pebbles and beetles. I also didn't work on any building projects besides the dam, briars and mosaic (and the villagers themselves insisted on finishing the first hut. I also didn't have L3 Explore or L3 Medicine.

I bought L3 Medicine when my runner slowed down at 58, and just bout L3 Explore. I was pleased that my missing butterfly showed up soon after. So now this game just needs the last pebble and beetle!