Type 2 backstamps have C51 in a circle topped by a crown.
Type 2A and Type 2B coddlers have a reference number, R #561564 in a box below the circle. This mark has been seen on a coddler with a silver lid. Type 3 backstamps consist of the characters C51 in a circle topped by a crown.
According to KM, this would be an English registry mark, and if so, the design was registered in 1909 with the British Patent Office. The example shown has twenty dots, and so it's believed that the year of manufacture was 1911. Around the top of the circle are the words ROYAL WORCESTER. There are banners on either side of the circle in which the words CROWN and WARE appear.
Type 6 is a grouping of examples that we don't really know the chronology of yet. Type 6A has the same wording in the backstamp as Type 7 but in a larger type. Outside the circle appears ROYAL WORCESTER above and PORCELAIN below around the outside of the circle. The screw threads are of the newer, less-dense pitch.
The backstamp of Type 9 is black and is imprinted over the glaze. Here is a table backstamp characteristics of those similar types.
This coddler was probably manufactured for the restaurant trade. Here is a table backstamp characteristics of those similar types. The threads are the less dense (one or two threads on the lid, three or four on the rim of the top), newer style, as are all coddlers later than this type. Here is a table of backstamp characteristics of those similar types.