Well it is mainly Koeman's job, isn't it? Fuck me!
Not really no that's not his area. He might identify some players, he might discuss players with walsh and the scouting team but the recruitment of players isnt his responsibility or area. It's down to Walsh and the board so that is definitely their error in not getting a forward.
Unless they offered Koeman some late on and he said no, which given we got Valencia rather than do nothing last summer I doubt he would have declined someone rather than be left with what we have.