Merging backup folders in backups.backupdb deleting duplicates (time machine drive)

Grant is absolutely correct - the TimeMachine backup does not have duplicates. There is an original file and then all expressions of the file that appear in newer backups are links to the original. A link appears to the user like a file in every respect, unlike an alias, but it is not the file.

Time machine does not store duplicates of anything, unless the file with a particular name has changed. Each of the backups from particular date&time contains the files that have changed, and pointers to the other files that were not changed, but exist in an older backup.

You can not change the items in your Time Machine backup set, except with TimeMachine.app. If you try to, you will find that deleted items are stuck in the Trash, and cannot be deleted, and your backup set has lost its integrity.

Look at what you want to accomplish. Just attach that drive again and it will add the needed changes to reflect your drive today, based on what's already on the drive. When the drive is getting full, it will compress the oldest files into the next-oldest backup set and delete the oldest.

The only safe way to access TM backups is with TM. That said, access TM and use it to restore files starting with the oldest backups and working toward the newest.