-(label:[gmail-users]) works for me. but this is what I found out.
If there is a message in the conversation that isn't labeled, then it
shows up. For instance, I ran : gmail -(label:[gmail-users]) and a
few messages labeled [gmail-users] showed up. I looked at them and
there was someone who's name showed up and not the list...so I assume
his message didn't hit my filters... but as far as I can see
-(label:[gmail-users]) works