Registered inhabitants
The current number of inhabitants in the Netherlands is an estimate calculated by Statistics Netherlands. The figure refers to the residents in the Netherlands recorded in the municipal population registers. Although Statistics Netherlands receives daily information from the municipalities on all changes in the municipal registers, this does not mean that the current number of inhabitants is exactly known on a daily basis. First of all there is a short – and sometimes a longer – period between the moment that such a change takes place and the moment it is recorded in the register. In the case of a birth, this is usually a short period, but for immigration there might be quite a lapse. Asylumseekers, for example, are only registered after six months. Secondly, an unknown number of people are never recorded in the population registers because they do not have a residence permit, illegal immigrants for example. And thirdly Statistics Netherlands itself needs time to process the reports. Therefore the number of inhabitants calculated by Statistics Netherlands for a given moment is partly based on a estimate.

See: http://www.cbs.nl/en-bevolkingsteller.htm