Deduplicator not working in Local Folders

Started with my error:
I discovered my Local Folders/Trash folder contained an entire Folder-tree of messages, which must have happened inadvertently.

After I labouriously selected/dragged them back to their propper places, I realised the Trash instance was a copy, taken on a particular date.
So what I’d done was not recover stuff I’d deleted, but created tens of thousands of duplicates.

Unfortunately, Tools/Deduplicator does not fix my mistake.

I can select a single folder where I can SEE duplicates (identical timestamps and content, but the Tool finds No duplicates.

Am I missing something?

Thanks.
Mark