Has to be done in Original mode.
The License achievements do not stack, you have to get an S, A, B and C rank on seperate attempts.
The licenses are split by the money you make
S = $5000+
A = $4000-4999
B = $3000-3999
C = $2000-2999
To make this even easier you can go into settings and increase your starting time and lower the traffic difficulty and this won't affect the achievements