This particular can o' worms was opened
On Fri, 30 Jul 1993 17:22:44 -0500.  And we can blame it on "F.  Scott
Ophof" <[log in to unmask]>.
 
It's not exactly clear which point you're trying to address.  It seems
like you raised two issues:  (1) Minimizing the inconvenience of receiving
multiple copies of a message,  and (2) minimizing the chance of dropping
people out of the discussion when a poster edits the xpost list.
 
It doesn't seem like there's much you can do about (2) unless you can
get everyone to agree on which list(s) should carry the topic.
 
But as far as (1) goes, Usenet has adopted the method of enforcing
valid Message-Ids, and eliminating dups that way.  I've always had a
secret wish that MAIL/MAILBOOK would compare MsgIds to eliminate dups
on CMS.  If it did, then maybe more people would take advantage of
MB's MsgId option.  That wouldn't eliminate the *traffic*.  But at
least people wouldn't have to read/discard all the extra notes.
 
As long as that's not available, probably the best choice is (like
Eric said) to pick a list and make everyone subscribe who wants to
monitor the discussion.
 
But that can be inconvenient.  I've only had to do that once or twice,
but I do remember feeling put-out when it happened.  :-)
 
Bill