Lightroom :: Photos In Catalog And Cards - Suspected Duplicates -> EPIC FAIL

Scenario:  I'm out in the field filling memory cards and reviewing them on my secondary PC (laptop), marking & editing various images at night.  I do not manage to import all of the photos off of all of my cards (and can't due to disk space requirements).  I want to keep the edits and work (and images, due to running out of cards I formated some of them that I _knew_ were in the LR catalogue AND backed up onto other devices). 
 
I get home to my primary PC and export the laptop catalouge and then import it, WIN.  I start importing images from cards that ARE NOT IN THE CATALOUGE, also WIN.  I put in a card that has AT LEAST _SOME_ (but not necessarily all) images in the exported catalouge.  Lightroom FAILS to notice that images that were imported FROM THE SAME CARD into the Laptop & Desktop with THE SAME CATALOUGE are duplicates!
 
What I want to do is to BE SURE that all of my images are in my primary/desktop catalouge WITHOUT dupes.  I want to insert the memory card and have LR import ONLY THE ONES IT DOES NOT ALREADY have.  This seems like somehting LR should automagically support, but apparently not.  How do I accomplish what I want to do without doing something rediculous like importing everything regardless, then buying a de-duping tool, deleting the duplicate images using file system tools, then removing the not found images manually from LR?
 
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