Graphite was first discovered in Bavaria at the start of the 15th century.  The first pencils in Europe came about in 1564.

Large deposits of graphite were located in Borrowdale near Keswick in the Lake District in 1564, which lead to a thriving black market for the material.  Graphite was a preferred medium to lead, which was softer and produced fainter lines.  Originally,  graphite sticks were wrapped in string, later on, they were placed encased in hollowed-out wooden sticks.

Reference:

British Library. (2019). The History of the Pencil. Untold Lives Blog. https://blogs.bl.uk/untoldlives/2019/05/the-history-of-the-pencil.html

Tancia, Ltd. (2016). Now You See Me, Now You Don't: A History of Erasing. Pen2Paper. https://www.pens.co.uk/pen2paper/wp-content/uploads/2016/01/Now-You-See-Me.pdf

Prior to the 18th century, the most common medium for erasing graphite was bread crumbs.  To use bread as an eraser, you would cut off all the crusts, mash it into a ball and erase.  If you wanted to make it more abrasive, you can add powdered glass to it or fine sand.  I can't locate any documentation of adding these materials to bread, but it does help if you need impromptu fine sandpaper to sand out vellum.  Both materials would have been readily available to people, and their use in this manner is plausible. 

See video on the side to see how it was used.

Reference:

Faber-Castell. (2023).  Breadcrumbs Were Once Erasers. https://fabercastellusa.reamaze.com/kb/history-and-fun-facts/breadcrumbs-were-once-erasers-8aa1e923d7d8c282