Searching for something else I came across this recently (as you do) and thought it might be relevant to the castle. It’s from A Descriptive Catalogue of Early Charters relating to lands in and near Sheffield by T.W.Hall. It includes:
“a charter (prior to 1290) confirming a grant from Robert Young of Schefeld to Simon Halday of Schefeld, of one place of land with buildings in the town of Schefeld, which he held of Ralph de Wadesley, as it lay between the toft formerly of Richard Stivel on one side and the toft formerly of Rayner the cobbler on the other and it abutted upon the great road to the castle; and also one place of land, of the courtyard of him [the grantor], as it lay between the toft of the said Simon on one side and the toft formerly of the said Rayner on the other and it abutted at one end on the place of land which he [the grantor] had sold to the said Simon and at the other end on the garden of Matilda daughter of William the tanner and from the garden of the said Matilda extending to a certain curtain wall and thence to the east as far as the embattled wall of the courtyard, once Rayner’s, …” Hall notes that in 1270, Thomas de Furnival obtained from Henry III a charter that provided that he might build and fortify and embattle a castle of stone. Are the curtain wall and embattled wall part of Thomas’ new castle?