Importing already imported photos from iPhone to new computer

Just a thought: is it possible that the Apple ID associated with the ‘new’ account already has those ‘duplicate’ images on iCloud Photos? If so that would explain why the older shots wouldn’t transfer.

Anyway… Google Photos will upload all images from your iPhone, and from there you can access/download them to a desktop.

https://support.google.com/photos/answer/6193313

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