Danny Tan wrote:

>Why is Mozart's work starts with K--- instead of Op---? Are there any
>particular reason why he is special?

Indeed.  Mozart's works were never assigned opus numbers by publishers.  In
fact, if memory serves, he didn't see a great deal of his music published
in his lifetime.  The K stands for Koechel, who was the 19th century
musicologist that catalogued Mozart's work.

Kevin Sutton