You have to use yearly quantity for sale and making sales order from that?
If I undestand you, you have Blanket Sales Order for this solution. You need to put Quantities for all item from cotract. When you want to ship, you need to press "Make Order" and you will get Sales Order. On blanker order line, you will see original quantity, shipped quantity andinvoiced quantity analisys.
If you want to plan shipment on specific date/period, you can make more lines for the same item with different shipment date...
This is NAV standard. The same is in purchase.