The criteria for each degree of tipping is an ideal and there are many cats which visually fall between two ideals.
Although the genetic combinations are different; smoke = Inhibitor + Non-agouti while shaded/tipped = Inhibitor + Agouti, the variability of expression results in cats which seem intermediate in colour. This is a "two gene theory" where the two genes involved are the Inhibitor and the Agouti/Non-agouti genes. There are pet quality cats where the tipping is too heavy for it to be a well marked chinchilla, but too light for it to be a shaded silver. There are also shaded silvers dark enough to resemble the genetically different "light" black smoke. These differences are caused by various polygenes. This "two gene" theory is the one to be found in modern feline genetics texts. Before this interaction was understood, there was believed to be a recessive "chinchilla gene" which controlled the degree of tipping.
Before the genetics of these cats was well understood, the apparent continuous gradation between chinchilla through to smoke would have resulted in some matings between mis-identified cats. For some while, it was believed that Smoke, Shaded and Tipped were all variable effects of the same gene (or "factor" since the term "gene" was not in usage in the early days of cat breeding). This "one gene theory" seemed to be borne out by the fact that some Shaded cats were so dark as to be poorly marked Smokes, while Smokes occurred in a range of intensities from light (Masked Silver) through to dark (solid colour). And of course, the earliest shaded and chinchilla cats were seen to have come from mating tabbies with smokes.
In Tipped/Chinchilla and Shaded kittens, the tabby pattern may still be visible as it is the long hair which diffuses the colour. In Smoke shorthair cats, just as in many solid black cats, a tabby pattern is often still discernible in the form of ghost markings. This pet kitten appears to be a black smoke tabby and white (or a heavily marked shaded silver with white). In adulthood, the tabby markings will be obscured by his long fur. Smoke-and-white and Shaded-and-white are not colour varieties accepted by registries.
Those cats which meet neither the Chinchilla/Tipped nor the Shaded standard are still attractive pets.