I used to intern at Mars chocolate factories supply chain, and are familar with the cost of products such as Ferrero.
1. Overall Inventory Cost: From the supply chain perspective, there might be months ahead of procurement before the actual production of chocolate, so the decrease in cocoa materials will not reflect the overall cost soon and there fluctuations.
2. Raw Cocoa materials costs only takes a few of overall chocolate product costs. The sales, distribution, retails are large portion of the overall cost. For a typical Milk chocolate, the estimated cocoa material cost share of final retail price ~5–15%, Even Dark chocolate with high Cocoas the materials cost will only takes ~15–30% of the overall product prices.