It has come to my attention that if you talk in local chat in the wild and no one can hear you nothing is said. It happens in town but not in the wild/nether. Another thing is that in the wild/nether it says to use town chat even though town chat cannot be used by non-supporters. Nothing overly major, just small things
My understanding is that if no one can hear you, you get the message. If you do not get the message then 'someone' heard you. I also believe that if that 'someone' has /map hide set then they do not show up in a /c who.