A sanction regime is voluntary. JPN and SKR defied the US and invested in VN while there was a sanction regime from the US against VN. So if it is unfair to blame China for doing nothing to help NKR, then it is equally unfair to blame the US who maintains the sanction regime precisely because China and anyone else have the final freedom to assist NKR.
If the US is to blame for NKR's plight, then why not China equally to blame, especially since NKR is China's creation ?
If the US refuse to trade with X country because X President is left handed, would that refusal qualify as sanction ? If yes, then it means there is an obligation to trade, which is absurd. It removes the freedom and right to association.
Lol, funny you mention sanction and Iran, do you know in a period between 80s and 90s, where the US sanction runs high, the number one company in Iran is actually Coca-Cola? The fact that sanction does not do much, even to American company as they are just as easy to applies exemption with respect to the sanction to by-pass it? Not until Iran banned all Western Product, that is where the real sanction starts.
I am not saying China were off the blame list for the NK plight, nor US should be blamed for the sanction. Rather the point being, China have little to no influence to NK now, it's quite honestly useless to ask China to do anything on North Korea issue. Thus, whatever China do or don't do is basically a non-factor to the North Korean. In fact, NK is now turning into a Threat to China by day, as much as to South Korea.
For me? They asked for it. The Chinese did not think thru the action and consequence before activating their Foreign Policy to help North Korea, anyone think North Korean having nuclear power is a good thing should have their head examine. It's not about nuclear proliferation, but rather the intention. China could have stop the NK when it meant the most, they did not do it, now, they have a unstable country sitting next to it with a handful nuke they are indeed crazy enough to use it. You can see literally from the Chinese reception on NK issue how they are literally see NK as a threat.
Problem is, on the other hand, they could not do anything about it, any sort of procedure or action will most definitely resulting a deterioriating relationship between CHina and North Korea. Hence China currently is stuck.
Again, as I said, they asked for it.
I want to further discuss this but I have to go prepare my PhD Course which start in 2 weeks time. So, if you still think I have not answer your question, I will see what I can do with my merger free time at hand