I would use a quick LISP statement and see how many objects were selected.
(ssget "X" '((0 . "INSERT"))) will select all inserted blocks.
If you want specific inserts, select them by name using (ssget "X" '((2 . "name of block goes here")))
You can retrieve these using "P" in response to a "Select Objects:" prompt. You might also try setting the selections to a variable for easy retrieval after other things have been selected.
(setq SET1 (ssget "X" '((0 . "INSERT"))))
(setq SET2 (ssget "X" '((2 . "put blockname here"))))
Of course this method is old, but very powerful. You can do something like this using filters and just paying attention to the command line for feedback.