Missing cover in SLK 350 under the hood

Last week I discovered by chance that under the hood in the area of the vents a cover (in driving direction right , where the battery is located ) is missing. A call to the friendly one and he ordered me then this part with mounting material. According to the statement there are probably also models, which have no cover !? My model here allegedly does not belong to it. When I wanted to install it this evening, I noticed that there has never been a cover mounted. The drill holes are available, but no plug-in sockets into which the screws can be attached. I noticed the sockets, but why have never been there before? Could you check on occasion how this is with you?