I wish I could answer your question, but I don't have a clue. I have the same question myself, and hope someone will chime in.
I don't totally understand this, but I do know that when you take your nef into Photoshop and do some edits, and then save it back into LR, the psd or tiff that comes back will have a new 'date time' - modified date (different to the original nef) and will also record that it has been edited in Photoshop version x. You can see these changes in the Exif/IPTC panel in LR.
If I take the same psd/tiff back into Photoshop using the original and add another edit, it changes the 'date time' again in LR and the metadata status in the LR panel says 'uptodate'. I don't get the problem you are getting.
BUT I don't allow LR to automatically save out metadata to the my files: I uncheck that in Prefs.
If you allow metadata to be saved out to files in LR (either as sidecars to nefs, or straight into jpgs, psds, and tiffs), I'm guessing that that has something to do with your problem. I don't do it because I had problems with that many years ago, and solved those problems by not saving stuff out.
This may not help, but it does point you to the metadata that is being changed with each edit in PS.
Mel Hughes wrote:
I need a simple English answer, please. Internet search as well as calling/chatting with Adobe (you get India and the language difficulties are an issue) only add to my confusion
When I see this and know I've not used another app to change keywords or ratings or whatever, I just stay xxxxx it, I know Lr's metadata is right, and yes I do xxxxing want to overwrite whatever metadata's in the file.
If, for example, Photoshop has written editing history into the file, I know Lr will be writing its metadata to different fields.