I suppose, to borrow a phrase from the printing and photography businesses, there are "proofs" as well as "samples". A "sample" would be something passed out to the customer or even the pottery's outside salesmen to show potential customers the scope of a pottery's work. A "proof" would be more along the lines of an item presented to the customer for approval for a full run. I have a Syracuse Hotel Roanoke plate that doesn't seem to be documented anywhere. My thought is that it was a proposed design that never made it into production.
I don't think that RW collecting has advanced to such a state that "samples" and "proofs" command any additional value, with the exception of samples that show a bunch of different colors or topmarks. A sample of a single pattern seems to be worth about the same as any other piece of that pattern. The subject matter, pattern, and end user are more significant driving factors in value, rather than rarity.