> In the existing list's header (the new super list), you just add the
> Sub-Lists keyword pointing to your new sublist's name.
> (Super and Sub lists must be on the same machine)
>
> * Sub-Lists= Newlist
>
> Later if/as you add more sublists, you just add it to the super list's
> header like so...
>
> * Sub-Lists= Newlist, NewlistII, NewlistIII

If the superlist's archives are Private, then you'll want to change the
Notebook keyword too:

   Notebook= ...,Private,(Newlist),(NewlistII),(NewlistIII)

in order to give archive access to the sublist subscribers.

I think the same applies to Send=Private too.