It strikes me as incredibly weird to maintain two separate stacks, especially because FSD was "available" when I bought my car. In retrospect, though, I guess it wasn't actually available to use, just for purchase.

So I suppose they had a parallel development process for FSD while building autopilot features?

But since there is a hardware support overlap, it seems like at some point you'd migrate autopilot cars to the FSD software stack, with limitations added in via feature flags.