I wonder if those are truly mutually exclusive?

If a family unity could consist of up to 5 or 6, potentially more if it was a multi-generational home, and “at least one person per home” could read, that could be quite a low percentage point.

I guess it depends on what is meant by “almost nobody could read”, since that isn’t an exact figure. Does it mean 1%? 5%? 10%?