[1] The first version of the Sonata movement, completed around 1919 (although Ives stated in his "Memos" that it was actually "finished" in 1913), had many simplified passages, and omitted several passages that had been some of the "Centrifugal Cadenzas" of the Concerto (this version was published in 1921).
The passages that were retained in the Sonata movement that had been simplified were restored to their original state in the "Four Transcriptions from 'Emerson'" that were assembled between 1915 and c. 1923.
The Concerto was edited from all the extant sources: the existing Concerto sketches, the Sonata movement, the Studies, the Transcriptions, and verbal memoranda regarding the evolution of the music that Ives wrote as program notes to the Sonata movement.
The manuscript sources for each have many verbal memoranda that refer back to the original idea of the Concerto, identifying materials for piano cadenzas, and for specific orchestral instruments.
When Ives added the line back to the Sonata movement (in the copy of the Transcriptions made by copyist Reiss), in both pencil sketch and ink patch, he simply called it "viola part".