Studies of facial identity processing typically assess perception and/or recognition, with designs differing with respect to one important aspect: Target Prevalence. That is, some include “target absent” (TA) among “target present” (TP) trials. In visual search tasks, TA trials shift an observer’s decisional criterion towards a stricter one, increasing error rates. However, decisional biases will differ inter-individually and can change intra-individually as well. From one standpoint, excluding TA trials is logical as it ensures comparable levels of expectation, or decisional bias across observers, and tasks. However, in reality, TA trials may occur, e.g. in police line-ups, where it is important to consider observers’ face recognition ability independently for TA and TP trials. To our knowledge, the effect of including TA trials has not been systematically investigated in tests of face recognition. We sought to fill this void by testing different versions of the previously established Models Memory Test that measures old/new recognition of experimentally learned facial identities. Our study aimed to answer the open question of whether — and if, how — observer expectation matters in face recognition with naturalistic stimulus variations. We discuss implications for line-up scenarios that are simulated in research settings and occur regularly in policing.