Ann: GRR - Quarterly Report for 3 months ended 30 September 2018, page-14

Not a great quarter with the guesswork - most of which relates to production. Going through the figures:
1) Average sales price received predicted US$140.70/$A193.50/t against actual US$132.41/$A181.96/t. Reason/excuse: In the Port Kembla shipment there was 15kt of chips that wasn't predicted that dragged the overall average price down.
2) Unit cash operating costs predicted $A110/t against actual $A148.15/t. Reason/excuse: Error relates solely to concentrate production as I correctly estimated total of Mining & Production costs at $A59mil(535kt times $A110/t as against actual 399.4kt times $A148.15).
3) Concentrate production predicted 535kt as against actual 399.4kt. Reason/excuse: Big miss(135.6kt) as I thought second half of quarter would have been more normal production.
4) Cash and receivables predicted $A245mil as against actual $A233.7mil. Reason/excuse: Sales revenue down $A7.8mil($A101.3mil predicted v $93.5mil actual) due principally to pellets sold being down by 24.3kt. Property JV contribs up by $A4.7mil($A1.5mil predicted v $A6.2mil actual) due to Malvern Rd property settled early as it had previously been predicted in Mar19 quarter.
5) Pellet production predicted 575kt as against actual 437.3kt. Reason/excuse: Out by 137.7kt being near the same amount as concentrate production deficit.
6) Pellets sold predicted 523kt as against 498.7kt actual. Reason/excuse: A miss of 24.3kt due to Port Kembla shipment predicted as 53kt pellets but was actually 38kt pellets and 15kt chips. Parma Bulker shipment that left 23Aug was probably only 65kt as against 75kt predicted as they simply ran out of pellets to ship - this vessel was only in dock for little over a day which is the giveaway.
7) Pellet stockpile predicted 252kt as against actual 138.5kt. Reason/excuse: A miss of 113.5kt being pellet production deficit of 137.7kt less pellets sold deficit of 24.3kt.

So if you make a large error on concentrate production it will effect most other calculations but I don't think the shipping model/pricing is broken but I did have to increase the freight component to $US20 to reconcile to their figures.
Amended shipping schedule for the quarter attached.