Discovery of active hashnames within mesh?

[natevw]

The lost epoch headers are combined with the first 8 bytes of each mote's hashname to derive every mote-specific lost epoch. When lost or seeking a lost mote, a beacon with a minimum/zero length is transmitted during the mesh lost epoch to signal the mote's timing sync and current window (based on the frequency).

Is the implication here, that unless I already know a mote's hashname, I will not be able to communicate with it? (Perhaps this is already a given from a Telehash perspective? Am I remembering right that you need to have done some key-signing-party-type stuff before connecting?)

If so, then a mesh isn't really one big trusted "workgroup" which isn't too surprising, but then leads to the question of what distinguishes meshes from each other vs. just a global/public fabric? The willingness of motes to route only for/within that mesh?