Good thinking, somehow I hadn’t encountered the Consolidate Duplicates command before. I moved the media from the original and second import into a new project within the Production and selected Consolidate Duplicates, but nothing changed. I wonder if Premiere is seeing them as unique clips for some reason.
Here’s something interesting – I copied the project and opened it on its own (not as part of the Production) and running Consolidate Duplicates worked – so that means my issue has something to do with the Production.