duplicate copies

[Harry Putnam <reader@newsguy.com>]

I often copy news messages to similar named nnml groups to hold for a
while, study, refer to or whatever.  I've never managed to figure out
how to avoid copying duplicates to a group.

Imagine you read a thread and you want to hold the messages awhile,
then a week later you see there are 10 new messsages in the thread but
in reading them you get mixed up as to which ones you already kept, So
end up copying some more than once.

Short of memory improvement classes ( way to late for that) how can
gnus help me out?  

There is quite a lot about dups in the manual but all seems very
complicated and hard to follow.

The ideal solution for  this problem exists in another news reader
whos name I cannot say outload, but its initials are "Forte Agent".

There the user can throw a handful of messages at a group and will be
prompted as to whether they really want dups.  If you say "no" then the
ones that are dups don't get moved.  A handy way to sort it out.

Can gnus do something like that?