Since the 200th anniversary of its composition, the Symphony in G major (K. 45a.) has been the focus of only modest musical efforts, but it spawned a substantial musicological debate over attribution and style development that lasted decades, and even disturbed a planned series of complete recordings of Mozart's early symphonies. The problem lay in the difficulty of discerning the work of a highly precocious but very young Wolfgang from that of his highly skilled but less remarkable mentor and father, Leopold. Manuscript copies of the Symphony in G major were first discovered in 1923 at Lambach, a monastery in Northern Europe where the Mozarts often lodged en route between Vienna and their home base in Salzburg. Judging from its geographic location, scholars assumed the work had been written during a trip to Vienna in 1767-1768. This was generally accepted until 1964, when scholar Anna Amalie Abert proposed a new theory: that the K. 45a symphony was in fact Leopold's, and that a librarian at Lambach had mistaken the work for another one by Wolfgang, in the same key; the manuscript for this other symphony, known as G16, was also housed at Lambach. Abert argued that K. 45a exhibited several traits closer to the style of the elder Mozart, such as a monothematic structure in the Allegro maestoso first movement; extensive strings of sequences and/or short, perfunctory phrases; and, in the gallant second-movement Andante and the Presto triple-meter finale, a rather uninventive motivic development. G16, on the other hand, seemed to Abert to unfold in a more fluid and creative fashion. So convincing was Abert's argument that in a recording series of the complete Wolfgang symphonies undertaken by Christopher Hogwood and the Academy of Ancient Music, G16, the "Neue Lambacher," was included, while K. 45a, the "Alte Lambacher," was not. In an advisory capacity for the series, however, Neal Zaslaw concluded in 1982—too late to change the recording schedule—that the K. 45a was indeed Wolfgang's, while G16 was Leopold's. According to Zaslaw, the somewhat archaic traits on which Abert based her attribution, as well as its three-movement structure (as opposed to the four-movement form favored in Vienna), placed K. 45a within the younger composer's oeuvre, but earlier in his chronology; it is now generally thought to have been composed in the Hague in 1766—when Mozart was only ten years old.

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