With the completion of a rough draft of the Agnus Dei and Dona nobis pacem occurring roughly about this time, musicologist Barry Cooper estimates that by now Beethoven has a more or less complete first draft of the Missa Solemnis.
It is not, however, by any means the finished work. In between a series of illnesses, he will continue to work on the Mass, often making major changes, off and on over the next 18 months. In particular, the Agnus Dei and Dona nobis pacem will be significantly different in their final form, with different marches interrupting the piece in varying places. The Dona nobis will initially be set in 3/4 time, and then go through variants in 6/8, 6/4 and 12/8 time, before Beethoven finally settles on 6/8 with some consistency. Certain portions of the Credo (most notably the Crucifixus and Et resurrexit) will also undergo major and repeated revisions during this time, especially during the summer of 1821.
The final version of the Agnus Dei section of the Missa Solemnis is here performed by John Eliot Gardiner, conducting the Orchestre Révolutionnaire et Romantique and Monteverdi Choir.