Corporations use an accounting method called FIFO..first in, first out. So, every product's price is raised to reflect the replacement cost, regardless of when the original product was purchased. This accounts for the cost of carrying the inventory (maybe for a year or two), the opportunity cost (what they could have done with the money they have invested), and a certain amount of overhead.
This is more info than you may have wanted, but it's how corporations work. The same applies to gas prices when they are going up.