Early Models of WTC II
The early models of WTC II survive only in non-autographic sources from between late the 1720s and late 1730s. Eleven movements of the total forty eight currently survive, of which three movements are transmitted in two different versions. It is estimated that many more movements once existed in early versions. However, many fragmental ideas from these are still recognisable, mainly in the sources of Tradition A.
The surviving early models can be classified into three categories:
those stemming from a collection of five short and simple preludes and fugues (BWV 870a, BWV 899-902), which are arranged in ascending diatonic key from C to G: the system Bach also used for Clavierbüchlein for Wilhelm Friedemann Bach (1720). This Group is represented by two contemporary sources, P 804 and P 1089, in the hand of Bach's close circle, Johann Peter Kellner (1705-1772) and Johann Caspar Vogler (1696-1763) respectively;
those appearing in a collection of pieces but without having a clear structural function as such Go.S.19, P 563, P 226, etc.;
those gathered together bearing evidence of WTC II already being prepared -- P595, by the hand of Johann Friedrich Agricola (1720-1774), who became Bach's pupil in 1738.