Help with understanding DepMap Cell line summary

When I type in a cell line, on the right there is a column Header that says “Molecular Subtypes”.

Under this it will often say “Level 0”, and under that it might say “CDKN2A-Lof”. What does Level 0 refer too? Also, how is the CDKN2A-lof (I assume loss of function) determined. In some of the cell lines I am looking at there is certainly no loss of CDKN2A mRNA and no mutations are listed. What is up with that? Thanks for your help.