D&E almost always used a built in pin back for standard brooches and pin/pendants.

 They would use a one piece pin back if it was a small figural brooch, small bar brooch, or a small medal type brooch. Very very rarely if the construction of the brooch just did not allow for a place to solder on the built in pin back they would also use a one piece pin back.  

I have shown examples of the types of brooches that they would use one piece pin backs on.

So a fairly good rule is a regular brooch, without a built in pin back is NOT D&E.