There seems to be alt.binaries.x & alt.binaries.X (well at least in my groups list - which I just did a complete download).
When adding alt.binaries.x in NBP, it adds both. Well it check marks both, but I only see one in Groups list.
I'm using: frugalnews, astraweb, usenetexpress.
Not sure if .X is valid, or if you need to handle case sensitive groups?