What year was the first published score of the piece that was completed in 24 days issued?
The music for Messiah was completed in 24 days of swift composition. Having received Jennens's text some time after 10 July 1741, Handel began work on it on 22 August. His records show that he had completed Part I in outline by 28 August, Part II by 6 September and Part III by 12 September, followed by two days of "filling up" to produce the finished work on 14 September. The autograph score's 259 pages show some signs of haste such as blots, scratchings-out, unfilled bars and other uncorrected errors, but according to the music scholar Richard Luckett the number of errors is remarkably small in a document of this length. The original manuscript for Messiah is now held in the British Library's music collection. It is scored for 2 trumpets, timpani, 2 oboes, 2 violins, viola, and basso continuo (cello, double bass, and harpsichord).
At the end of his manuscript Handel wrote the letters "SDG"—Soli Deo Gloria, "To God alone the glory". This inscription, taken with the speed of composition, has encouraged belief in the apocryphal story that Handel wrote the music in a fervour of divine inspiration in which, as he wrote the "Hallelujah" chorus,  "he saw all heaven before him". Burrows points out that many of Handel's operas, of comparable length and structure to Messiah, were composed within similar timescales between theatrical seasons. The effort of writing so much music in so short a time was not unusual for Handel and his contemporaries; Handel commenced his next oratorio, Samson, within a week of finishing Messiah, and completed his draft of this new work in a month. In accordance with his frequent practice when writing new works, Handel adapted existing compositions for use in Messiah, in this case drawing on two recently completed Italian duets and one written twenty years previously. Thus, Se tu non-lasci amore from 1722 became the basis of "O Death, where is thy sting?"; "His yoke is easy" and "And he shall purify" were drawn from Quel fior che alla'ride (July 1741), "Unto us a child is born" and "All we like sheep" from Nò, di voi non-vo' fidarmi (July 1741). Handel's instrumentation in the score is often imprecise, again in line with contemporary convention, where the use of certain instruments and combinations was assumed and did not need to be written down by the composer; later copyists would fill in the details.Before the first performance Handel made numerous revisions to his manuscript score, in part to match the forces available for the 1742 Dublin premiere; it is probable that his work was not performed as originally conceived in his lifetime. Between 1742 and 1754 he continued to revise and recompose individual movements, sometimes to suit the requirements of particular singers. The first published score of Messiah was issued in 1767, eight years after Handel's death, though this was based on relatively early manuscripts and included none of Handel's later revisions.
1767