Most of Mozart's compositions had not been printed and published during his lifetime. Many different people had the manuscripts of one or another work. Often there were no copies other than the original manuscript in Wolfgang's own hand. We know that unfortunately some of his works have been lost because of this, and in fact from time to time works of Mozart are still being discovered that were previously unknown.

Yes, the boxes represent some important periods in Mozart's life and work, and important groups of compositions that he wrote during those periods. The boxes are

• Wolferl's First Compositions, Starting in 1761
• The Five Violin Concertos, 1775
• Piano Compositions from Vienna, Starting in 1781
• The Late Symphonies, 1788
• Mozart's Greatest Operas
  
  The Marriage of Figaro
  Don Giovanni
  The Magic Flute
  
• The Last Concertos, From 1791