Data Retention - Sales Information

I have many Sales Orders that are decades old and the original price list doesn’t show anymore on the sales order. I created a dashboard and confirms nothing there. Is there a retention limit on how long a sales order can be on the system before it doesn’t appear anymore? Does anyone know how I can restore the Price List to the sales order? If there is a way?

I would also like to know if there is retention time limit on Sales Order information. If anyone knows what the basic good practices that should be implemented. I would appreciate it.

Thanks in Advance