sentence: Research depends upon the earliest printed copies.
sentences_before: The original manuscript does not exist.
sentences_after: Some pieces are believed missing. Sometimes music Purcell composed in the middle 1680s is put into the score to balance the loss. Sometimes the missing music is composed completely afresh in Purcell's style.
concept_name: research
headings: Dido and Aeneas Musical numbers
categories: 17th century operas