Edition: Laura Youens, Messzyklen der frühprotestantischen Kirche in Leipzig, Münchner Editionen zur Musikgeschichte, 5 (Tutzing: Hans Schneider, 1984), 73-111.
The earliest source for this five-part Mass is the Alamire manuscript MunBS 6 which (judging from its repertoire) dates from the 1520s. The Mass is anonymous here, as it is in LeipU 49 (c.1558), and the ascription to Josquin comes only in the much later set of partbooks RosU 49, copied in 1566. This has made it an easy target for Josquin scholarship, which in the New Grove worklist has rejected the Mass on the grounds: counterpoint and texture untypical. Without the attribution my guess would have been that this was a setting by Pierre de La Rue. Yet it is important to keep an open mind as to the range of stylistic choices that were open to Josquin in his final years.
I have followed the MunBS 6 readings except where these were clearly and uniquely in error. Based on plainchant sequence. No model in Wegman.