This is not a new issue at all and plenty of other posts reference the problem. After importing all old photos into one collection, plenty of images are duplicated because EXIF data was changed or deleted from various copies. Lightroom cannot tell that two images are identical because their resolution or EXIF data may differ. I'm forced to rely on 3rd party tools like dupeGuru or Picasa which pollutes folders with hidden data files. I can manually tag every single photo with people and event names, and then compare each tag manually to see if there are duplicates. Yet for a collection of 22k photos, that's an unreasonable task to perform. Photoshop Elements 2 already has this technology and that program is years old. When will this be added to Lightroom?
When will this be added to Lightroom?
We're not Adobe employees here, we are just Lightroom users.
So the only answer we can give you is ... um ... we don't know when this will be added to Lightroom. We don't even know IF this will ever be added to Lightroom.
Perhaps you should submit a formal feature request. Photoshop Family Customer Community, but even if you do that, you won't find out "when"