In this manuscript we consider an important topic in official statistics, namely estimating the number of usual residents. For the Netherlands we investigate the under coverage of the Population Register. First, the Population Register is linked to an Employment Register and a Crime Suspects Register. Then, we use three list capture-recapture methodology to estimate the number of usual residents. Two problems arise: 1) all three registers have no variable on usual residence; 2) capture-recapture methodology relies on a couple of assumptions, for which it cannot be verified whether they are met. The paper shows how the problems are solved.