What you are talking about is what LISTS do, not what topics do.
Topics are topics, lists are lists.
 
A feature of VM/CMS's version of LISTSERV is subscription to a
file.  When updated, LISTSERV can either send the file to the
file-subscriber or send a message that the file has been changed.
This is called AFD and FUI respectively.
 
Thus, if you have some sort of monthly posting that you'd rather
not send to all subscribers, but still make it available to
interested subscribers, use the AFD/FUI mechanism.  Of course you
could obviate the need for FUI by broadcasting a short note to
all list subscribers that the file has been replaced.
 
Instructions on subscription/retrieval could be part of your
WELCOME file.  That's how we do it on the lists that I
co-operate.
 
--  co-owner:   INFOSYS, TQM-L, CPARK-L, ERAPPA-L, JANITORS, LDBASE-L, et -L
URL:mailto:[log in to unmask] "Never confuse the messenger with the message"