Silly question: How do you do multiple conversions from RAW? Is that an embedded JPG within the RAW file?
Just that Lightroom just overwrites the previous JPG for me, replacing the whole file rather than updating it. I don't use embedded JPGs though, I just publish when needed.
My RAW files on the other hand will show multiple edits on multiple days. I take the photo, I load it into Lightroom (which changes it), I apply my own changes, I may come back another day and apply other changes. I may make a virtual copy so that I can have two different photographs from the same RAW (e.g. different crops, B&W vs Colour, different contrast curvers, etc).
No idea how any of that impacts the XMP data though :)