Currently the unArchiver will ignore the same file queued additional times. As if the user were to keep opening the archive from Finder. It's already in the queue so it's ignored.
How about with multipart archives, do the same thing, so that when working with scripting that would essentially do the same thing as opening all the parts. the unArvchiver already parses for multipart archives- in that you can open any one part and it will start at part1 regardless.
Can this somehow go through the same check that it's doing on multiple instances of a single file?
This would allow for drag and drop of the whole download directory and have each archive processed once, instead of adding to the queue once for each part. As it is now, the user has to individually select one part from each set and open/drop that on the icon to avoid queueing multi-part archives multiple times.
Making a rule for the automator to only act on the file entry if the name ends in either *.rar or *.part1.rar .. would be ridiculously nasty. Likewise, looking for *n.rar where n is a number would mean the most common naming scheme on a file would cause it to be ignored.
FileName.Version.n.rar .. where n is the version number.
The same issue is mentioned here and marked Fixed, but .. it's not, or at least not totally.
https://code.google.com/archive/p/theunarchiver/issues/255