Ann: Financial Year 2019 Results Presentation, page-25

You're cherry picking your figures. The latest (and therefore more accurate) figures were a sale price of $450 per tonne, not the average of $502 across the year. Likewise, last costs were $406 per tonne produced, not $393 across the year. I know that it's not an enormous difference, it's still a healthy stockpile, but in the interests of credibility I'd stick with the figures from the latest quarterly. Particularly when the short-term outlook isn't looking too rosy due to the coronavirus.