How does Royal Mail integration update stock figures on Shopify?

32 2 12

We are about to integrate Shopify with Royal Mail Click and Drop to fulfil distribution for a unisex T-shirt that appears in 2 products within our store. For historical reasons, we use the same SKU for both products. When we mark as despatched on Click and Drop, there's an option to mark as fulfilled and update the stock figures on Shopify. Does anyone know if this will be done via SKU and change the value in 2 places, or only update a single location? Our current distribution centre integration kicks back and updates stock figures in both locations...

Thanks