All Orders has the ability to show you items where they are needed. For example if you buy items for production but never sell them, why should the be on the sales order. Whether an item shows in a SO, PO or WO depends on its GROUP and particularly the IsSold, IsPurchased and IsUsed flags as follows:
IsSold: Quote, Sales Order, Ship Doc
IsPurchased: Purchase Order, Receiver
IsUsed: Work Order