Class I and class II (we shouldn't really use 1 or 2) can only refer to the product / appliance not the cable. As stated above cable does not actually comply as class II, even though it may indeed have two independent layers of insulation.
The current approach is to protect for a single fault, that's the whole principle of the wiring regulations, and pretty much all other associated standards - IEC 61140 included.
Thus class I if the insulation fails, it uses ads - there is no further faults considered, as a product you don't supply additional earthing arrangements etc to cover the case that the cpc isn't connected.
Similarly class II if the insulation fails, it is a second layer of insulation (or reinforced) - no further faults are considered.
If the cable enters a class II product without sufficient protection to ensure compliance with class II, then it is a poorly made product, or not compliant at all i.e. a cheap knock-off - it doesn't mean that the principles of product classes is incorrect