Models about customer lifetime value (CLV) explicitly or implicitly assume a “one-firm oneproduct” environment. We show empirically what problems occur when CLV models are used within a multi-product company. In 99.9% of the cases the summation of the product specific CLVs do not equal the directly estimated CLVs on product portfolio level. When CLVs are used to differentiate between customers, top customers on an aggregated portfolio level differ in more than 20% if estimation approaches are changed. The use of CLVs on product basis only, leads further to a systematic neglect of 30% of a firm’s true best customers.