2019 Nickel outlook, page-480

Quite right.
it doesnt account for all metals as i have alluded too ...there are off market stockpiles but all metal that are to be traded LME through its regulatory compliance has to be notified before a contract is issued. The mere fact that Tsiangsin is taking all its metal through the lme would indicate that there is limited access to off exchange supply.
Either way the deficit is loosely linked to stockpile and is definately a good indicator of future pricing trend.
btw i have heard the Ni sulphate contract could be just around the corner.