Your concept of the flooring may be contingent upon the material being used.

Could it not have been a wood floor? Certainly that would have been obvious to the robbers as being "not stone", and therefore might have something under it. And, it would have been destroyed over the centuries as torch material, scavenged wood, etc.

It has been postulated by several Egyptologists that the rooms we see are not how they appeared originally... they might have had fine gilded walls, or wooden walls with intricate carvings (including texts, perhaps?) and that these items would have been removed a long, long time ago.

These are just thoughts on the subject. Nothing definitive.

Anthony

You can lead a horse to water but you can't make him think.