We use LR5 to shoot tethered on sets which sometimes crashes and both the camera and LR have to be restarted (a whole different issue...). When this happens, some images that were being transferred dont get copied to the hard drive or catalog. The next step would to just import the raw files from the CF card. Within the import settings the checkbox to suspect duplicates is selected, however not a single image is suspected as a duplicate when all but the few that I'm trying to import are!
We do add a preset while tethering but I wouldnt assume it would add to the file size.