Behind a great deal of preserved work there is somebody whose name went unrecorded. They copied, prepared, corrected, and kept the materials, and their hands are on every page that survived while the credit went to one person. The contribution is genuinely invisible, not because it was hidden but because the conventions of recording never had a place for it.

It is worth assuming, in any impressive body of work, that there were more people involved than the record names. In your own work, name them explicitly. Attribution costs you almost nothing and it is one of the few things that does not survive by accident.