I think I see the problem. I tried to recreate the USB installer, but step 10 does not happen.
http://www.osxlatitude.com/edp/documentation/pre-installation/
10. Next, you will be prompted about Extra folder; choose “Use My Own†from the list then browse to your downloaded bootpack (i.e. Extra) folder.
It never prompted me to "Use My Own", so I'm not able to add my own extras. This is why I was thinking I needed to replace the extras folder with that of the pack. Perhaps, they folder needs to be merged? Advice?