As per my observation 55 Kg cylinder accommodate around 7.5-8 Kg on 200 bar pressure
My previous car with 50 Kg cylinder mostly filled with 7 kg (+,- .25) on 200 bar pressure. I think these figures will help you for reference.
Everybody please note that landi ranzo TN1-SIC, TN1 kits have maximum high pressure value capacity upto 220 bars. Now a days many CNG stations have 240 pressure which may be dangerous if you ask him to Full the Cylinder. Cylinder tolerate the pressure or not, but CNG kit and pipes may be damaged at this pressure.