The Legacy Achievement: Have 10 or more generations in one household

I actually have 6/10 generations in one family, but the achievement counter says there are five. Is this because I didn't witness the demise of the sims in the first generation?

Here's the in-game tree:
https://farm2.staticflickr.com/1722/42600900892_3dd3028bc8_o.png

There are two babies in sixth generation, but little Parker McConnell- Aidan's son- is two days older than his father's cousin's son.