This is one of a series of postings of important classical music dates, from the 17th century to the present. Included are the date and location of the birth and death of composers, and the premiere date and location of the first public performance of works. When the premiere date and location is unknown, the date or year of completion of the work is given. Though reasonably comprehensive, this is a subjective list, so the choice of composers and works is mine. If you find any errors, or if you can offer a premiere date and location for a work where only the completion date or year is listed, please post a comment here.
1770
December 16 – Ludwig van Beethoven (1770-1827) was born in Bonn, Germany
1771
Wolfgang Amadeus Mozart (1756-1791) completed Divertimento in E flat, K. 113
1772
Giovanni Battista Sammartini (1700?-1775) almost certainly completed Symphony in F Major (J-C 36) by this year, probably much earlier
Joseph Haydn (1732-1809) completed Symphony No. 45 in F♯ minor, Hob. I:45 “Farewell”
1773
April 16 – Wolfgang Amadeus Mozart (1756-1791) completed Symphony No. 27 in G major, K. 199/161b
October 5 – Wolfgang Amadeus Mozart (1756-1791) completed Symphony No. 25 in G minor, K. 183/173dB
1775
Wolfgang Amadeus Mozart (1756-1791) completed Violin Concerto No. 5 in A major, K. 219
January 15 – Giovanni Battista Sammartini (1700?-1775) died in Milan, Italy
September 12 – Wolfgang Amadeus Mozart (1756-1791) completed Violin Concerto No. 3 in G major, K. 216
1778
Joseph Haydn (1732-1809) completed Piano Sonata in E minor, Hob. 16:34
Wolfgang Amadeus Mozart (1756-1791) completed Violin Sonata No. 21 in E minor, K. 304 (300c)