Later models do not carry these backstamps. Although exact date of production is unknown, due to the backstamp and design & condition of the case, we believe this set to be one of the earliest production (early-mid 1960's) and older than other Y6235 cups & saucers available online. If you search online you will see the difference.
The item "Box Set of Spode England Bone China Y6235 Colonel Blue Gold Trim Tea Coffee Cup" is in sale since Tuesday, June 26, 2018. This item is in the category "Pottery & Glass\Pottery & China\China & Dinnerware\Spode\Porcelain". The seller is "sgol2901" and is located in Manassas, Virginia. This item can be shipped to United States.