After 39 posts I just know that “metadata” is a complete mess, not only in DxO PL but in general it’s a bad idea to trust a “standard” which turns out to be only valid for parts of certain apps which give hilarious examples for incompatibility. DxO with it’s lack of colour labels, with it’s messy mixture of DOP, XMP, and a database which apparently is only good enough to be deleted a.s.a.p. is a very good example how messy things get when a company wants to include all needs of users but already fails in developing a clear and communicated concept. I’m put off that rubbish.
Dear @CaptainPO you are totally right.
I made here a genuine and humble remark, nothing more, nothing less 
Sounds good.
A great DAM should be able to do this.
The one I use does this. It is able to read MD from the original files but it will not write back to the original files (except .dng and .jpg).
Anyway, I know DxO is very busy and we are here to test, share and comment.
Personally I am fine using an external tool today for my workflow.
The perfect software to make everybody happy at the same time is yet to be created on Earth 