A sales forecast that is based solely on shipment history is a method that uses past sales data to predict future sales. This method assumes that the sales pattern will remain consistent over time, and does not account for any changes or fluctuations in demand or supply1. Therefore, this method can be distorted by any factors that affect the availability or delivery of the products, such as material shortages.

Material shortages are situations where the supply of raw materials, components, or finished goods is insufficient to meet the demand. Material shortages can be caused by various reasons, such as natural disasters, supplier issues, transportation disruptions, quality problems, or demand spikes2. Material shortages can have a negative impact on the sales forecast that is based solely on shipment history, because they can reduce the amount of products that can be shipped to customers, and thus lower the sales revenue. Material shortages can also create a backlog of orders that cannot be fulfilled in time, and thus create a gap between the actual and forecasted sales3.

The other factors listed in the question typically would not distort a sales forecast that is based solely on shipment history, because they do not affect the shipment history directly. Labor rate changes are changes in the wages or salaries paid to workers. They may affect the production costs and profits, but not necessarily the sales volume or revenue4. Currency exchange rates are the rates at which one currency can be exchanged for another. They may affect the competitiveness and profitability of international sales, but not necessarily the sales volume or revenue5. Customer demands are the needs and preferences of customers for products or services. They may affect the sales potential and market share, but not necessarily the sales volume or revenue.