My husband earned commission on items he purchased for inventory for sale. The amount of commission was a percentage of the profit determined when it was sold (buy low, sell for higher amount). He did not sell items, just purchased them and then collected

My husband was a purchaser of inventory. His job was to get a good deal for the inventory, and then when someone else in the company sold that particular item, he earned a commission on the percentage of profit determined by the sale price (minus the buy price). He purchased many items for his company before he left. Since then, they have been selling those items for a profit but are refusing to give him commission for anything sold after he left. He did the work of purchasing the inventory (per his job). Shouldn't he get the commission when the sales occur and the company profits from the sale of the inventory he purchased?