Product retention in public corp. (White Giant)

What is the maximum amount of product that a public corp. can have in stock?

I know that 10 % of the stock should get sold if it's more than 12 months production but I see some corporation's that don't sell any of the products.

Can somebody tell me why that is?
Thank you

There is no maximum.
Be careful not to let your corp get into too much debt though!