Here’s a really quick, simple tool to keep in mind when trying to figure out which blocks are referenced in a drawing, and how many times each is referenced. Use the Express Tool BCOUNT. It is not on any menus or ribbon panels; it is only available through the Command Line.
This command has two simple options. Press ENTER after you issue the command, and you get a text list of all block references, and a tally of the number of references for each. If you PICK a block after issuing the command, you get a tally of how many references there are for that particular block.
Of course, you can see a list of all block definitions in a drawing from the drop-down list in the BLOCK or INSERT dialog boxes, but this is a list of all blocks available in the drawing, regardless of whether or not they are referenced.
Remember, many blocks can exist in in a drawing (as Block Definitions), but may not actually be used in that drawing (as Block References). The BCOUNT command can help you determine whether there are blocks defined in a finished drawing that can safely be purged (deleted). It can also be used for quick and simple reporting on quantities of objects in a model, such as how many manholes or valves there are.