In studies on the composition of prophetic literature, the larger textual layers reinterpreting earlier texts, the so-called Fortschreibungen, received much attention. It is well-known that beside these larger literary elaborations prophetic books also contain shorter explanatory interpolations, often called glosses, which intend to clarify a particular imagery of the prophecy (e.g., Isa 9:14). A systematic reading of these short annotations has been neglected, however, in studying the formation of prophetic books. The present article reconsiders the Isaiah-Memoir from this perspective. It identifies editorial interpolations in three distinct pericopes, Isa 8:2, 8:6-7a and 8:23b. It is argued here that the identification of such explanatory additions is the key to understanding notorious textual complexities. Moreover, it points out that these interpolations tend to expose recognisable patterns and common hermeneutical principles. Unlike Fortschreibungen, however, these interpolations are not concerned with the reapplication of the prophecy to the era of the editor, but they intend to guide the reader in understanding the prophecies in their original historical setting.