To make the difference clear:

• NONE means that Poser will look for a file only in the exact location and runtime you actually have selected. Useful for content creators to check whether all files are where they belong, but that's it
• DEEP means that Poser will browse ALL currently registered runtimes, but that takes time. However, if the search returns None you may be quite positive that the file definitely is missing.
• SHALLOW ... never was quite sure about what Poser does with this option... Does it only search in random places, depending on time or barometric pressure? Or does it toss some dice? Who knows?

So use "DEEP" in order to look for a specific file.

Your rants about the Poser search function I can't comment because I've never used it. I prefer the normal OS search function because it'll also find files which were accidentally placed outside the Poser runtime structures.