In the 1990s Sadie began completing Mozart aria fragments. During that decade he tried at different times to get some of them performed in the United Kingdom and in the United States but was not successful. In the late 1990s Sadie became involved in the Classical Opera Company, directed by Ian Page. On 17 September 2003 Sadie's versions of 'Giunse il momento alfine... Non tardar, amato bene' (K492) and 'In te spero, oh sposo amato', (K440/383h) were premiered at St. John's Smith Square. In the following year, on 23 July 2004, the Classical Opera Company gave a concert performance at St. John's Smith Square of 'Mitridate' using three arias reconstructed by Sadie: 'Se di lauri il crine adorno', 'Lungi da te, mio bene' and 'Nel grave tormento'. At the Cossington Mozart Festival in September 2006, the Classical Opera Company again performed Sadie's versions of 'Giunse il momento alfine... Non tardar, amato bene' (K492) and 'In te spero, oh sposo amato', (K440/383h) as well as Sadie's version of 'Müßt ich auch durch tausend Drachen (K435/416b).
Sadie's completions of Mozart aria fragments were published posthumously by A-R Editions, Inc. in 2012.
Contains, correspondence, music manuscripts, concert programmes and press cuttings of performance reviews.

See MS Add.10095/19/6 for CD-ROM recordings of the Mozart aria fragments performed by the Classical Opera Company.