Occasionally problems can arise with search results in Spotlight. This is caused by the search index getting corrupt. When searching for something, Spotlight doesn’t search every file on your computer, that would take way to long. What happens instead, is that all the contents on your computer is added to an index, the Spotlight Index. This includes meta tag data, every word inside your documents, emails… and pretty much everything else.
It’s not unheard of for Spotlight to have some issues, and keeping track of the constant ever changing data on your computer has been known to trip it up every now and then. Sometimes when search for something, Spotlight may refuse to acknowledge it’s existence, even if you’re blatantly staring at in on your desktop.
Also, if you’re having issues with it taking a long time, these methods will also speed up Spotlight search.