14.04, was once thought to have been composed by Wolfgang Amadeus Mozart, but is now considered to be the work of Johann Friedrich Eck [ca] (1767–1838).
A common hypothesis made in the later half of the 19th century was that the piece was based on authentic Mozart material but constructed by a less skilled composer.
Cecil B. Oldman believed that the work had stylistic similarities to Mozart's sinfonia concertante for violin and viola, K. 364, and that Eck was the completer of the work, writing in a footnote to p. 1469 of The Letters of Mozart and his Family Volume III: This is the Concerto in E♭ (K. 268), the authenticity of which has so often been debated.
It was reviewed in the AMZ for October 1799 and curtly dismissed as an incompetent piece of work, which could not possibly be by Mozart.
On the strength of Ernst's testimony, which is far from unambiguous but clearly associates the work with Munich and with the Munich violinist Johann Friedrich Eck, the present writer has argued that in the form in which it now survives it represents Eck's working over of Mozartian material, and has suggested 1780–1781 as the date of its composition.