It is both really. If a 'breed' cannot fulfil the criteria the RBST established as a viable, historic breed, then they can't consider whether it's rare or not. Poultry is a whole different ball game as there is no pedigree record as such. It takes quite a few generations of sometimes intense in-breeding to establish a new 'breed' of cattle, sheep, pigs etc. and no breed exists today of any domestic quadruped which is the result of a simple cross between two existing breeds. This is why, for instance, the attempts by certain individuals to recreate breeds such as the Cumberland, Ulster Large White and Lincolnshire Curly Coat will never come to anything meaningful. They might manage to create a lookalike but that is as close as they can get. It's no nearer the real thing than a tribute band or an impressionist on TV and can never be without a detailed knowledge of the building blocks and exact replication of the breeding that went into the original. As that was never recorded and most of the building blocks themselves have changed or disappeared completely, it is a futile effort that can achieve nothing.