Immediately after Süssmayr had completed the requiem and before the delivery score was given to Count Walsegg, Constanze’s friend Abbé Maximilian Stadler also made a copy of the requiem. It exists in two copies, one in the Stadtund Universitätsbibliothek, Frankfurt am Main (Mus. Hs. 211) and one in the Austrian National Library (Cod. 19. 057). These manuscripts are so interwoven that one must have originally been part of another. Stadler had given a copy to the publisher Johann Anton André on 21 August 1828; it contained the Sequence as far as the end of Confutatis.
Stadler must have copied Mozart’s fragment not once, but two times; otherwise, he would not have given one copy away. However, it appears that he only have one copy of the Introit and Kyrie, explaining why he did not give these parts to André. Therefore, the copy in Vienna is more complete.
Stadler also made a separate copy of the Offertory. This copy was also given to André, and it ended up in the Austrian National Library in 1931. The attempts, in Stadler’s handwriting, to orchestrate the Offertory, have forced us to ask a question: Did Stadler copy some of Süssmayr’s orchestration, or did he first try to complete the section before handing it over to Süssmayr?
There is no evidence that Stadler had received the score soon after Eybler gave up his completion. However, it something of this sort did happen, then Stadler must have been on of the unidentified composers Constanze had turned to after Eybler quit, before contacting Süssmayr, who eventually took charge of the entire completion.
However, these copies by Stadler were most likely made after Süssmayr’s completion. If this is indeed what happened, then Stadler must have attempted to re-complete it after Süssmayr finished, not before.
So Constanze’s “unidentified composers” still remain unidentified even after two hundred years of musicological research.