Kirk - thanks for the ideas. It seems like it *should* work, but isn't in practice.
I've tested with a couple individual images by clicking the Info button for the photo in the browser to bring up the IPTC Info panel for that photo, then clicking "Load...", and selecting the photo's XMP file - this has worked properly in a couple of cases, but not all (though all attempts end up with a "doubled" caption, for some reason).
However, using your suggestion (I just checked the Urgency field in the IPTC Stationery Pad, and set it to "Normal" - not something I've ever used in the past) doesn't succeed in embedding the keywords from the XMP sidecar file into the RAW file. I've tried setting "When writing IPTC/XMP" for TIFF-based RAW photos to "Add embedded IPTC", with no success. Also checking "Add embedded IPTC4XMP" made no difference. Also, after trying this process, photos that I tried embedding IPTC individually with success previously (through the IPTC Info Panel) no longer work for some reason.
Not sure if this is related, but should PM show the keywords from the XMP sidecar file in the IPTC Info Panel? I have set "When reading IPTC/XMP" for TIFF-based RAW photos to 1st - Read XMP sidecar file, 2nd - Read embedded IPTC, and 3rd - Read embedded XMP, but the keywords never show up for photos in which they aren't embedded.
Are there any other settings I should be checking in this process?
Thanks again for the help!
Rick