Great responses, thanks. It looks like the 2 and 4 pin housings I ordered were from the KK series, while the 3-pin housings were from the CST series. When I went to order the crimp contacts, I grabbed contacts that were associated with the CST series, not the KK series.
I've decided to go with bare male headers so that the housings don't need to be polarized or have anything fancy on them (locking ramps, friction lock, etc.). I found housings such as the following in the KK 2695 series: http://www.digikey.com/product-detail/en/22-01-2031/WM1576-ND/1090454
The following crimp pins are in the Associated Products list: http://www.digikey.com/product-detail/en/0008500113/WM1114CT-ND/467980
But the crimp pins are in series KK 2759 series. I have a hunch that the numbers are less indicative than the letters (KK), but does anyone know for sure what that naming scheme is about?