if the resolved pathname exists then it is used , no searching done , but it looks like Poser searches the default runtime , then the others in the order they were added. In python thats poser.Libraries().     Then Poser searches , and may the good fairy sprinkle you with happy dust if you have many silver.jpg or anything else that arent exact duplicates.    

Content providers could use Daz Studio to test file referances , because it doesnt search , if the file isnt where the relative path says you get an error .