Smelling is one of our several senses, so usually when one senses something it is registered or detected, this is "by definition." Now your question is interesting because you question hinges on "deep philosophical thought." You have probably hear the following question before, "If a tree fell in a distance forest and no one heard it, did it actually fall?" That is, no one heard the sound of the fall, so did it actually happen? Was a sound actually made?
Will, lets compare this to the smell of "natural gas." That is, the gas that is used in kitchens' cooking, gas ranges. That gas, as it naturally exists, that is as it comes, directly from Nature, "has no smell." However, a compound that has a characteristic smell, that we associate with natural gas, is added to the gas so that we can smell it, for safety's sake, just in case we happen to develop a gas leak in our system (or leave the gas on somehow.
Now, the question is, "Does natural gas actually have its own smell and our olfactory sensors simply cannot register it?
I don't know the answer to this question. It would make a good subject for a hub.
Take care, rdlang05. As a matter of fact, it just occurred to me. Let's make this one a hub. Maybe it will stimulate other readers or writers to investigate this matter further.
Have a wonderful day, rdlang05.