one simple answer.
Old vitz = Simple Automatic Transmission (CNG Compatible)
New Vitz = CVT i.e constant variable trasmission (CNG not compatible at ALLLLLL)
Now for CNG convertible japanese cars here is the list.
1) trious Kid 660 cc (better cng on non turbo one)
2) All japanese 660 cc (better be manual and non turbo)
3) All japanese cars having non CVT transmission
CNG non Compatible
1) Vitz 2005 onwards
2) toyota passo (all years)
3) All japanese cars with CVT