It is not about mileage per tank. It is about mileage per kg of CNG.
Pump pressures and gas temperatures vary. And also, CNG pressures are in bars in Pakistan and not in psi.
At 200 bar and 20 degree C, standard 50 liter cylinder will get 8.8 kg of CNG.
But if pressure is higher or gas is colder, more kg can enter tank.
One pump in my vicinity has 300+ pressure on sunday as surrounding industries are closed. On a cold sunday, with 340 bar pressure, I got 14 kg filled in 50 liter tank. This is extremely dangerous, and tank was at its limit, but I didnt know this at that time. Preferably, get 8 kg filled for safety in a 50 liter tank. And at maximum, 9 kg. Never more than that.
If you people compare km per kg instead of km per tank, I am sure there will not be much difference in results.