Template update allows to modify the biometric reference of a user while he uses the biometric system. With such kind of mechanism the authors expect the biometric system uses always an up-to-date representation of the user, by capturing his intra-class (temporary or permanent) variability. Although several studies exist in the literature, there is no commonly adopted evaluation scheme. This does not ease the comparison of the different systems of the literature. In this paper, they show that using different evaluation procedures can lead in different, and contradictory, interpretations of the results. They use a keystroke dynamics (which is a modality suffering of template ageing quickly) template update system on a dataset consisting of height different sessions to illustrate this point.