Duplicated images on iCloud Photos

I’m seeing thousands of “duplicate” images on iCloud photos…and I’ve no idea where they are coming from.

- Some are duplicated images with same file name but the file type has been appended to .jpg, where the original file has .JPG

- Some are images with an “old” file name which the original image no longer has.

All are images that at some point previously have been on an iOS device, but the images no longer exist anywhere.

I’ve only ever used iCloud photos for creating shared albums, & have never backed up any device to iCloud.

The history:

Recently decided to migrate all my photos to iCloud, bought myself some storage space and uploaded/imported photos into Photos app on my MBP 10.11.6, went through tagging names to Faces, then discovered this version of Photos doesn’t sync with iOS devices. (Not too worry)

After I had completed the import - whilst redoing name/face tagging on iOS device, I noticed some duplicate images I deleted a few & then realised there were lots...hundreds/thousands. So I attempted to resolve it, by going back to MBP and…

1) deleted ALL photos from iCloud - emptied the DELETED folder

2) Turned off iCloud Photos on all devices (MBP & 2x iOS)

3) Deleted all photos on all devices

4) Signed out of iCloud photos on all devices

5) Trashed Photos app library file on MBP

Then the re-install:

7) checked original source folders for any duplicates, renamed, edited etc and trashed any potential conflicts

8) on a clean install Mac Mini 10.13.6 > never had any photos on it or been associated with iCloud account

9) trashed the Photos app library

10) imported my source photos folders one by one into Photos App

Should be all good… but in the All Photos / Moments view I’m seeing thousands of images that shouldn’t be there. They are all valid photos that at some point have been synced to an iOS device, but they shouldn’t exist any longer.

At the moment I’m going through 30,000 photos in the “All Photos” view - comparing which image is in the original album, inserting a “DESCRIPTION” against all photos in the album, then going back to “All Photos” view and deleting any images from the album that don’t contain a “DESCRIPTION”. This is extremely tedious and time consuming, but I don’t see any other way of resolving it.

Why? Where are they coming from?

Advice appreciated.