Thanks, that's definitely good news. When I changed my settings to those in the manual, xmp side card files were produced by LR, leading me to believe that they were necessary to the communication between PM and LR. Previous to changing those settings, LR didn't produce xmp cards. I'll try running through the settings again but if you have any guesses here, your input would be much appreciated.
ETA: For example, this from the manual is unclear to me: "You must also use XMP sidecar files with your RAW files when working with Adobe products."