In verification step,
1st step simplify verify Ref2, if result is not match, go to 2nd step.
2nd step is excluding last 1 digit and compare again. If still not match go to 3rd step.
3rd step excluding the last two digits to compare, if this last step still not match then it’s invalid number.
Note : as the last two digits are transaction code i.e. Rental, registration or Insurance and the Bill payment type.