Karnaugh Veitch diagram and ordering of the variables
The lower K-map is wrong:

      A
  0 0 1 1
D 1     0
  1     1 c
  0 1 1 1
     B 


It can better be drawn as:

       A
    0 0 1 1
  0 _ _ _ _ 0
D 1 _ _ _ _ 0
  1 _ _ _ _ 1 C
  0 _ _ _ _ 1
    0 1 1 0
       B


The goal is to have a unique combination of variables for each cell in the matrix. It doesn't really matter which variable goes where, as long as you get the distribution right. For both horizontal axis you can either use:


(top) | (bottom)
0011 and 0110


or


1100 and 0110


or


0011 and 1001


or 


1100 and 1001


or 


0110 and 0011


or


1001 and 0011


or


0110 and 1100


or 


1001 and 1100


As long as you carefully check which combination of variables is related to every single cell. Same goes for the vertical two axis.