Here is a description of the way I manage Play Raws:
There are, first, seven steps on setting up additional instances of dt. After the seventh step there is explanation, beginning with, “By using memory for the library, you will not create a database. By setting storage to Never, you will not overwrite the xmps you open to examine.”
Below that I describe my system for managing xmps. It describes how I keep track of duplicates. Maybe that will be of help to you.