Almost thirty years ago John Morehen noted the presence of a common hand in four important pre-Commonwealth sources of sacred music: Pembroke College, Cambridge MSS Mus. 6.1–6 (six part-books; hereafter Cpc 6.1–6); St George's Chapel, Windsor MSS 18–20 (three partbooks; WRch 18–20); British Library, Harley MS 4142 (a wordbook; Lbl Harl. 4142); and Christ Church, Oxford Mus. 1220–4 (five partbooks; Och 1220–4). All four sources appeared to date from the early 1640s. Morehen also observed that the same scribe subsequently copied the earliest post-Restoration part-books at Windsor (WRch 1 and 2). Identifying the copyist(s) is a crucial stage in the study of the sources, with important implications for provenance, date and function, as well as their authority relative to other sources of the period.