Most everyone knows of the standard Royal Doulton production figurines with numbers like HN 1362 Pantalettes, but there are other figurines available, including original model and specialty figurines.  Original model pieces are always marked on the bottom as being "Property of Royal Doulton", while specialty pieces may have only the backstamp of Royal Doulton.  Most of the famous sculptors of Royal Doulton produced specialty pieces of which fewer than 500 pieces would have been made.  For whatever reason, these pieces were chosen not to be production pieces and instead were given as gifts or sold locally in England.  Most of these specialty pieces are in the hands of collectors that would not ever part with them, however some occasionally come to market through Estate Sales and other means.  A Specialty piece or Original Model would significantly raise the value of a collection when present.